INTERDISCIPLINARY PROJECT
JANUARY 2015
DISHWASHER DINNER
Growing Cucumbers on Dishwater from the Eurest
Canteen on Science Park; with the use of a Wastewater
Plant System.
Teuntje Hollaar
10167617
Toon Maassen
10279261
Laura van Veller
10419306
Yorick Vink
10164103
Lucas van der Zee
10295461
Supervisor: Mw. dr. M.F. Hamers
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ndsupervisor: Dhr. dr. K.F. Rijsdijk
Institute for Interdisciplinary Studies (IIS)
University of Amsterdam
Track: BSc Future Planet Studies, major in Earth Science, Physics, Political
Science, Human Geography and Chemistry respectively
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University of Amsterdam
Content
Abstract 3 Introduction 4 Metabolic Rift 4 Gaps of knowledge & Research Question 5 Justification for an interdisciplinary approach 6 Theoretical background 7 Green Urbanism 7 Wastewater Treatment 7 Social acceptance theory 8 Liebig’s Law 9 Methodology 10 Experimental Methodology 10 Experiment set-up 10 Water collection 11 Determining the water flow 11 Chemical water analyses 12 Composition of control group 12 Adjustment of dishwater 13 Removal of nutrients from dishwater 13 Social methodology 14 Consumer Acceptance 14 Producer acceptance 14 Results 15 Potential consumer interview 15 Consumer interview part one 15 Consumer interview part two 15 Consumer interview part three 16 Producer interview 17 Plant analysis 17 Nutrient removal 18 Discussion 19 Technical discussion 19 Conclusion 20 Social conclusion 20 Technical conclusion 20 Integrated conclusion 21 Literature 22 Appendix 24 Components of detergent 24 Stakeholder interview Eurest 24 Matlab script Statistics 27 Survey consumer 303
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Abstract
Expansion of the capitalists modes of the production, industrialization, urbanization and the displacement of small scale agriculture has led to the metabolic rift. Urban agriculture, as element of Green Urbanism, represents the main method used to overcome this separation of humans from the ‘fruits of their labor’. This research explores a hydroponic system, which reuses wastewater and thereby recycles the macronutrients Nitrogen and Phosphorus. The specie Cucumis Sativus is produced within this system. Three hydroponic systems are constructed: one containing wastewater, the second containing the Hoagland solution and the third system containing the Hoagland solution with adjusted N and P levels. To ascertain implementation of the waste water plant system (WWPS) on the Science Park Amsterdam Campus, an interview has been carried out to investigate the acceptance by the producer and a questionnaire was answered by potential consumers to investigate their acceptance. The results show that the plants cannot grow using dishwater as sole source of water and nutrients, although not due to a lack of macronutrients. This shows that if these nutrients could be recycled in a manner less harmful the plants, cucumbers could be grown on dishwater. The acceptance towards the WWPS is high, from both producer and consumer in the Science Park community. The WWPS does not closes the metabolic rift, due to the interposition of the producer. An interconnect of the consumers and the producer is needed to overcome this social rift. Nevertheless, the actual willingness on both ends is present, so when the technical implications are resolved, the WWPS can be embedded in society and the environmental rift on Science Park could be closed.
Metabolic rift recycling grey water waste water plant system (WWPS) Science Park Amsterdam
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Introduction
In this report a small step will be taken in the larger journey towards a sustainable society. A socially embedded system to recycle nutrients from wastewater for food production will be investigated.
We believe that the unsustainable elements in society are rooted in a metabolic rift. This concept will be explained to elucidate the relevance of ‘urban agriculture’ styled solutions.
Second, the need for this research will be explained by giving an insight into previous research on this topic, showing which gaps of knowledge are yet to be filled. This will end in the research question with its sub-questions. These are partially disciplinary, but all lead to an interdisciplinary conclusion, which is further explained in the ‘justification for the interdisciplinary approach’. In the following chapters, the methodology of the empirical research and social research will be specified ending with results and their discussion.
Metabolic Rift
Due to the expansion of the capitalist modes of production, industrialisation, urbanization and the displacement of small scale agriculture, a divide between human and nature has occurred (Marx, 1976). This divide is noticeable within the natural as well as the social and individual sphere and is sometimes referred to as metabolic rift (McClinock, 2010).
With the commodification and thereby consolidation of land and the emergence of new farming technologies, an environmental rift occurred (McClinock, 2010). Because the demand for agricultural labour decreased, farmers were displaced from their land into the city for industrial work. Also, the production of food got more in the hands of capitalists and less in the hands of families. Thereby the production and consumption of food got separated. (Magdoff & Forster, 2000). In this search for ongoing accumulation, the previous sustainable biophysical relationships got disrupted. Crops and livestock were separated, causing exhaustion of the soil and therefore a dependence on synthetic fertilizers. In order to fertilize the soil and to optimize production, finite resources are mined and natural gas and petroleum are used to produce the fertilizers. These millions of years old fossil fuels are shipped and used miles from the point of extraction (McClintock, 2010). At the moment, global phosphate demand reaches 148 million tonnes of rock per year (Cordell et al., 2009). This phosphate is mostly exported by Morocco and China. These known phosphate reserves are expected to run out in the coming fifty to a hundred years (Cordell et al., 2009). The metabolic rift also has implications on the social sphere. Not only did humans partly cause this rift, but also did it influence them in their being. Because humans did no longer consume what they produced, they got separated from the fruits of their labour. Within the production process most of the people were only responsible for a little part like screwing in a screw for instance. This made that they could no longer identify themselves with their work (McClintock, 2010). The rift had also its cultural aspects, as McClintock states: ‘’The socio-cultural significance of food and agriculture rarely factors into calculations of profit margins; certain social relations woven into the agri-food system—for example agricultural and culinary knowledge and its cultural significance— are impossible to quantify and either resist commodification or are erased by a commodified agri-food system” (McClintock, 2010). One way to soften the problem of the metabolic rift is by the fusion of town and country. According to Marx: The present poisoning of the air, water and land can be put an end to only by the fusion of town and country; and only such fusion will change the situation of the masses now languishing in the towns, and enable their excrement to be used for the production of plants instead of for the production of disease. (Marx and Engels, 1978, 723).
One method for the fusion of town and country is Urban Agriculture (UA). Urban agriculture is the activity of growing food in and around a city, town or village and is a part of Green Urbanism (Lehman, 2011). In the Global North this way of agriculture is one that is seen as a way to encourage urban sustainability (McClintock, 2010). According to McClintock (2010) Urban Agriculture has the potential to soften the metabolic rift, because UA causes the closing of nutrient cycles, the de-alienation of humans from the biophysical environment and the de-commodifying of food.
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Gaps of knowledge & Research Question
The aim of this research is to contribute to the solution of the metabolic rift. In this research a new way of processing urban grey water for the purpose of food is explored. The research will focus on the Netherlands, because the metabolic rift can be clearly seen in Dutch agriculture; especially its use of artificial fertilizer, and household water use. With one of the world's highest population density, the Netherlands produces a lot of domestic wastewater. On average a household produces more than 120 litre wastewater a day. Large amounts of water are needed for the use of toilets and washing machines, but also cooking of dinner and doing dishes contribute to the large amount of wastewater per household (Rijkswaterstaat, 2014). Currently, this water is treated and fed back into the natural water cycle at a location separated from where the water is wasted. Domestic wastewater contains high values of pollutants and macro nutrients. Two types of domestic wastewater exists: grey water and black water. Black water contains faecal matter and urine, also known as sewage. Grey water or sullage, is generated from all other domestic sources and mainly exists of soap residues. About 70% of the 120 litre wastewater produced a day per Dutch household is grey wastewater (Rijkswaterstaat, 2014). Grey water contains a lot less pathogenic bacteria comparing to black water and is therefore easier to recycle in a small scale system. Within the biophysical dimension the larger aim of this research is to assess the regaining of nutrients P and N from municipal grey wastewater. Sullage can be seen as a potential source of nutrients for agriculture instead of waste that has to be treated and still has potential to damage the environment. So, if this system succeeds in the production of crops, regional food production also increases food availability. To test the potential for food production, an experiment will be devised using cucumber plants (Cucumis sativus), which is selected because of their considerable nutrient need, fast germination and the large body of scientific literature around the species. Within the social dimension, this research will mainly focus on the effects of the wastewater plant system on human behaviour. Not only the de-commodification and de-alienation of food will be addressed, but also the degree of social acceptance will be examined. A gap in knowledge exists around the implementation of this system in society. Multiple researches have been carried out on grey water irrigation in communities in developing nations, however, there is little research about implementation of novel, urban agriculture styled, water systems in developed nations. Our research question therefore will be: How can a socially embedded food production system contribute to closing the metabolic rift on Science Park Amsterdam by recycling nitrogen and phosphorous from dishwater to grow Cucumis sativus?
Food production by nutrient recycling is investigated with a hydroponic system in which cucumber plants are grown and monitored for length. The water will be checked for pH, nitrogen (NH3, NO3-) and phosphorous (PO43-)
and salinity. This food production system is embedded in a social system; the users of science park will be questioned about the level of social acceptance towards the technique and in-depth interviews will be held with the staff of the Eurest Science Park canteen. These inquiries must lead to a deepened understanding of the metabolic rift and possible ways of closing it.
Natural Science
• What is the ideal composition of water for hydroponic production of cucumber plants? • Is the water from the Eurest and Polder canteen suitable for cucumber production in terms of nutrient availability (nitrogen and phosphorus) and pH? • What is the chemical composition of the dishwater from the Eurest canteen science park • To what extent are the nutrients from the dishwater absorbed by the plants? • What is the composition of the dishwater when it leaves the system?
Social Science
• What is the level of social acceptance of a nutrient retrieval system? • How can the social acceptance possibly be enhanced?
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• What is the contribution of the wastewater plant system to the reunification of people with the fruits of their labour?
Justification for an interdisciplinary approach
The problem addressed in this report is complex and problem-based. More than two disciplines are needed to offer insight in the question at hand. The idea of a nutrient reclamation facility with the help of plants is a technical solution to a social problem. To understand the disciplines involved with this research we have set up a diagram describing the situation at hand in our research. This is represented in figure 1. The center of our theoretical research setting is formed by the more technical disciplines; Physics, Bio-Chemistry and Earth Sciences. These disciplines will work closely together, identifying the best way in which the facility can be constructed and operated. Around the center is the discipline of Human Geography. This discipline will focus on the social acceptance and implementation of the solution in the specific area, being Science Park Amsterdam. Intensive conversation and reflection with the team at the center is needed to further understand the social and technical implications at hand. This will help to come to a reflexive strategy to heighten social acceptance of the technical solution posed by the team. The all-encompassing discipline is Political Science. This discipline will focus on the effect of the solution on the divide between man and nature. The changes because of the solutions posed by the reflexive work by both the center and secondary circle will have serious impact on this divide. One can see that the diagram represent a big picture in which all disciplines have to work closely together and influence each other’s work in a reflexive and dynamic manner.
Figure 1: Map of Different Disciplines
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Theoretical background
Before diving into the details of this research it is important to introduce several important theories and concepts that are used to conduct this research. The most essential are the following:
Green Urbanism
The concept that is being used in order to build this research on, is the concept of Green Urbanism (Lehman, 2011). This concept arose in the 1990’s in the USA in order to promote socially and environmentally sustainable cities which are compact, energy-efficient and have zero-emission and zero-waste. It also focuses on adjusting the relation between nature and city. As we now live in an era of uncertainties, where water, food and energy are scarce, Green Urbanism is committed to minimize the use of these resources (Lehmann, 2010). Green urbanism is mostly used as a tool to re-engineer urban areas with a holistic approach to create more sustainable cities. In order to create these cities, a set of principles are designed. One of these principles is sustainable waste management. An objective of this management is turning urban waste into resources, another is local food and short supply-chains. Part of this principle is Urban Agriculture which can function as a bridge for the disconnection between city and country (Lehmann, 2010).
Wastewater Treatment
When browsing the technical literature on wastewater, it seems that a definition of the concept ‘wastewater’ is rarely found. Subtypes, such as industrial or domestic wastewater are identified, variation in chemical composition, as well as the many different ways to dispose the chemicals are discussed in detail, but a clear definition of wastewater is not given (Gray, 1989). Wikipedia gives the following definition: ‘Wastewater is any water that has been adversely affected in quality by anthropogenic influence.’(Wikipedia, 2014). A representative example of a definition of wastewater treatment in the technical literature is the following: ´Biological wastewater treatment involves the transformation of dissolved and suspended organic
contaminants to biomass and evolved gases (CO2, CH4, N2 and SO2) which are separable from the treated waters. Excess biomass produced within processes must be disposed´ (Low & Chase, p. 1120, 1999). These examples of wastewater definitions seem to merely focus on the word ´waste´ in ´wastewater ´. Clearly the assumption is that the water contains unwanted substances which must be disposed before the water can enter the water cycle again. Although there is a strong movement in science and engineering to reuse compounds found in the wastewater streams, quite some research about nutrients, especially nitrogen, seems to focus on the disposal of these substances. On the contrary, agricultural sciences take great efforts in preserving nutrients in watery solutions and growing media (Hofstra and Bouwman, 2005). Astonishingly, the molecular composition in agricultural nutrient solutions do show resemblances to that of wastewaters; both contain micro- and macro nutrients needed for plant growth (figure 1). A major difference between the two forms of water is that wastewater may also contain chemicals and organisms that are hazardous for plants and animals. Additionally, the nutrient levels in fertilizers are usually adapted to meet the needs of the specific crops they are used on, while the composition of wastewaters can vary greatly in time and space. (Gray, 1989).
Although using wastewater and other wastes in agriculture is a old practice, the documentation of nutrient recycling and development of novel techniques is of a more recent time. Citations referring to the use of wastewater for irrigation go back at least to 1967 (Pennypacker, Sopper, Kardos) and possibly further. After this, lots of research has been conducted into the effects of using wastewater for irrigation of agricultural land. From the 1970s, novel techniques were investigated for the combined production of mussel or oyster and algae in wastewaters (Rither et al. 1972). Another focus was the use of algae grown on nutriënt holding wastewater, for the production of biodiesel (Pittman, Dean, Osundenko, 2011). The synchronous cleaning of wastewater and use of its nutrients for growing food crops has been researched by Boyden and Rababah (1996). However, this research ignores the health risks of bacterial contamination and heavy metal collection in the plants that is associated with municipal wastewater (Rosas, Baez, Coutino, 1984). Other researchers have focussed on the health effects of irrigation with either grey- or wastewater, only not in combination with water purification. This is where a gap of knowledge is present; there is no system investigated in which grey water is used in a system that has the combined goal of providing nutrients for food crops, providing water for food crops and providing (partially) cleaned water. The advantage of using grey water over municipal wastewater is that it is expected to contain a far lower level of pathogens.
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Social acceptance theory
Practical policy literature makes much use of the term social acceptance, but clear definitions are rarely given. It is sometimes stated to be just an aggregation of multiple concepts of acceptance and not really a unifying holistic theory, but for the sake of this report we will support the theory side. To clarify the term Wüstenhagen et all. (2007) distinguishes three dimensions of social acceptance, namely; community acceptance, socio-political acceptance and market acceptance. All three, sometimes interdependent categories of social acceptance are of importance with social acceptance of services.
One of the most important concepts is ‘environmental attitude’. The concept of environmental attitude was first used by Maloney and Ward in 1973. In their paper called Ecology, let’s hear it from the People. An objective Scale for Measurement of the Ecological attitudes and Knowledge they talk about the relation between the attitude of people and their willing to act to and accept environmentally friendly principles of living. They state that, assuming that someone’s behaviour is generally part of a particular behavioural pattern, which is based on values and attitudes, a real solution can only be achieved by a radical change in mentality, followed by a change of critical behaviour on a population-wide scale (Maloney & Ward, 1973). They believe that if one wants people to change their behaviour, they need to change their environmental attitude. This can be achieved by informing the public of environmental issues. Yet further research indicated that the environmental attitude of people was not strongly linked with environmentally friendly behaviour. In 1975 the theory of reasoned action (TRA) was coined by Fishbein and Ajzen. It makes use of the attitude concept stated earlier but formulates the relation between action and attitude differently. In this theory attitudes are based on a combination of evaluations of attributes of, and beliefs about the object of study. However, the attitude does not directly influence behaviour; instead it directly influences a behavioural intention (Fishbein & Ajzen, 1975). But not only attitudes are influencing the intention. There are social norms, constructed from beliefs from the collective of family which might prove to be a barrier between the attitude and the intention (figure 1). Behavioural intentions have a direct influence on actual action. But also here barriers are involved. Per example; one might have the intention (caused by attributes and beliefs) to separately dispose of plastics and non-plastics but if there are no such disposal sites, he will still dispose of it in the same way. Research using this theory indicates that there is hardly a connection between the general notion of ‘environmental attitude’ and a concrete decision. The theory of reasoned action has been used in many cases and has supported many policy decisions (Tellegen & Wolsink, 2006). Still, not everyone agrees with the theory’s practica assumptions.
Figure 2: Model of TRA
The validity of the theory of reasoned action is questioned in recent literature on environmental decision making. For example Thogersen (1996) pointed out that some decisions concerning the environment are made in a more altruistic psychological environment. He states that:
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Expected utility models cannot be fruitfully applied to all the diverse kinds of decisions and activities with which people cope” (Thogersen, 1996).
Among others, Thogersen argues that for certain kinds of behaviour the altruistic dimension is of more importance than the reflecting subjective utility dimension used in TRA. He argues, after a literature research, that for example participation in recycling schemes is better explained by the altruistic dimension of environmental values than by TRA like attitudes.
Liebig’s Law of the minimum
‘Growth of any organism is controlled not by the total amount of resources available, but by the scarcest resource in the system.’ The Law of the minimum stated in 1840 that the rate of the growth of a plant, the size to which it grows, and its overall health depends on the amount of the scarcest of its essential nutrients that is available to it. Carl van Sprengel (1828) was one of the first to discover that plants feed on nitrogen compounds and carbon dioxide derived from the air, as well as on minerals of the soil. Though, it was Justus von Liebig who disseminated the theory. During the agricultural revolution, Liebig’s Law was often used to support the fertiliser industry. Though, due to large amounts of fertilizer supplied to agricultural fields, the amount of nutrients is often not the scarcest resource in the system anymore. Liebig’s theory is applicable to the fact that phosphorus is an important nutrients for all primary production. Phosphorus will be depleted within 50-100 years (Cordel, 2009) due to anthropogenic activity. This makes phosphorus an essential and scarce nutrient, so if not already it probably becomes a limiting factor in primary production. Also the growth rate of Cucumis sativus will depend on the availability of the scarcest of the essential nutrients present in the dishwater.
Methodology
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In this chapter both the experimental as well as the social methodology will be explained. All the actions involved with carrying out the research will be discussed in this chapter.
Experimental Methodology
In order to test the possibility of using dishwater to produce food, the research entails an empirical part in which cucumber plants (Cucumis sativus) are grown on perlite, a soilless medium, through which dishwater flows. Cucumber plants are chosen, because of the extensive body of literature associated with the species. Studies have shown that high yields are achieved with perlite hydroponic systems. Moreover, perlite has a neutral pH and is sterile (Wilson, 1984). Dishwater contains less nutrients than black water. Therefore the main question of the empirical research is, whether it is possible to use the little nutrients present in the dishwater, to grow food. Additionally from the values obtained from the research conclusions can be drawn about the extent in which nutrients are removed by the waste water plant system (WWPS).
Experiment set-up
Three WWPS’s were built: one holds 6 cucumber plants on the dishwater from the university canteen. The other two systems, each holding 3 plants, were control groups, using clean water with chemical fertilizers. The first control group was supplied with the Hoagland solution (Hoagland & Arnon 1950), which contains all the nutrients most commonly applied to hydroponically grown plants. The other solution contains the same phosphor and nitrogen concentrations as measured in the wastewater. In this way we are able to compare the results of the cucumbers growing on wastewater, with a completely conventional hydroponics system and a system which contains the same nitrogen and phosphorus concentrations of the wastewater, but does not contain all the other substances in wastewater, and which is sure to contain all the other kinds of nutrients needed.
The laboratory set-up consists of three hydroponics systems. Every system consists of three containers, one containing the dishwater, one containing the perlite and the growing cucumber plants and one receiving the outgoing water. The plants are grown on perlite hydroponic medium as described in Trajkova, Papadantonakis & Savvas (2006). Perlite, a processed volcanic glass, is a commonly used medium for hydroponics for it is able to hold high amounts of water and hardly reacts with other substances. A peristaltic pump pumped the water through a tube from the dishwater container to the container containing the plants. The container containing the plants has a hole at a height of 10 cm through which the water can escape to the third container. In order to prevent the perlite particles from clogging the tubes, a cotton filter was built in front of the escaping tube.
Water collection
Before running the experiment, water was collected from the ‘Eurest Science Park’ and ‘Café-Restaurant de Polder’ dishwashers. These dishwashers circulate their water for half a day, after which the water is disposed into the sewage system. Water could be sampled at 15:00 or 19:30. The first series of measurements, on which the experimental set-up is based, used water sampled at 15:00. However, it is likely that the dishwater produced after diner (17:00 until 19:00) has a higher concentration of organic debris than the dishwater produced before 15:00. Unfortunately, the supposedly debris richer water could not be analysed sufficiently due to technical and financial reasons. During the experiment, water sampled at approximately 19:30 was used. The data obtained from analysing the 15:00 water has been assumed to be a lower limit and used to determine the minimal needed flow rate and synthetic wastewater composition. Because the volume of the dishwasher from ‘Café-Restaurant de Polder’ was insufficient, only water from ‘Eurest Science Park’ has been used.
Samples were taken after stirring the contents of the machine to create a homogenous distribution of solid particles. For the Eurest dishwasher, the first dishwasher along the conveyer belt was chosen. During the experiment, water was collected on Mondays and Thursdays and stored overnight. On Tuesdays and Fridays the water in the experimental set-up was disposed and replaced by the water collected the day before.
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In order to be able to determine the speed of the pump in combination with the used tubing, the pump was calibrated. The pump has a speed scale from 0 to 10. While measuring the time, 10 ml was pumped from one jar to the other, with the speed settings of 2,4,6, 8 and 10. The results of the calibration are shown in figure 3.
Setting
time (s)
speed (ml/s)
10 65
0.15
8 80
0.13
6 109
0.092
4 157
0.064
2 369
0.027
Figure 3: Calibration data of peristaltic pump
.
According to Harsharn et al. (2010) cucumbers in a hydroponics system need up to 188 liters water spread over 91 days. This irrigation water was applied during the crop growing period of which 116 L/plant was drained off and 72 L/plant was used to meet the crop water requirement during the growing period. This means a cucumber plant takes up 2 liters per plant per day. Therefore the 6-plant-system needs 12 liters per day (0,139 ml/s) and the 3-plant-system needs 6 liters per day (0,0694 ml/s). Using the calibration graph, this means setting 8 and setting 4 of the peristaltic pump. Another way to calculate the dishwater demand is to look at the nutrients. From Ingestad (1973) can be concluded that 1 plant consumes an average of 5,58 mg Nitrogen per day. If the 6 plants, having a nitrogen consumption of 35,1 mg/day, would take up all the nitrogen present in the water, 3,24 liter of fresh dishwater should be used every day, based on below described nitrogen levels . This would mean only 5,58 mg/plant/day, so if we grow 6 plants 33,48 mg/day. Seeing our nitrogen levels, this would mean that we would only need 2,07 L of fresh grey water every day to provide nutrients. However, from Ingestad (1973) can also be concluded that it is the nutrient concentration rather than the amount that is important for plant growth. In this article nutrient concentrations up to 500 mg N/l are reported to increase growth. concentration gets, the harder it is for a plant to take up the nutrients. Therefore the applied amount of dishwater is based on water demand rather than nutrient demand.Chemical analysis
Samples were centrifuged at 130000 rpm for 40 minutes. The sediment was collected and left to dry underneath the fume hood. The filtrate was also collected and analysed for NO32-, NH3/NH4+ and PO43- using Merck Millipore Nitrate, Ammonium and Phosphate test respectively. The sediment was not analyzed due to insufficient and inhomogeneous volume. The nitrate test reacts the nitrate ions with 2,6-dimethylphenol to create 4-nitro-2,6-dimethylphenol, which can be determined by photospectroscopy. The ammonium/ammonia test, reacts ammonia in an alkaline environment (ph 1-3) with hypochlorite and a substituted phenol to form a indo-phenol derivative, which can be determined by photospectroscopy. Samples were analysed immediately after preparation to prevent loss of NH3
The phosphate test reacts the orthophosphate ions in a sulphuric and acidic environment with molybdate ions to form molybdophosphoric acid which can be determined by photospectroscopy. A total N, total P and Kalium determination were taken of the samples. Samples were prepared as above and additionally filtered over a 0.2 micron membrane filter. Elemental phosphorous and nitrogen were measured to determine the total nitrogen and phosphorous contents of the water. The elements can emanate either from organic (food debris) or chemical sources (dishwashing soap). Elemental phosphorous was determined, together with Kalium using inductively coupled plasma atomic emission spectroscopy (ICP). Elemental nitrogen was determined using a Shimadzu total nitrogen unit, which thermally decomposes the sample and subsequently detects chemiluminescence of nitrogen compounds.
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C
Sample 1: de Polder
Sample 2: Eurest
EC (µScm-1)
678 1385 pH
8,70 10,61 Total N (mg/l)
5,055 10,82 NO3 -N (mg/l)*
8,5 8,1 NH3/NH4+-N (mg/l)*
5,0 6,0 PO4-P (mg/l)*
32,1 68 Total P (mg/l)
6,975 29,326 K (mg/l)
7,468 7,228 Figure 4: N, P and K levels, pH and EC of samples taken prior to running the experiment *Values were discarded because of interference of sample with analytical technique.
In both samples the measured nitrate and ammonia/ammonium (expressed in the weight/volume of the element) added up to more than the total N concentration. PO4-P measured by photospectroscopy also yielded higher results than ICP measurements. This leads to the suspicion that photo spectroscopic measurements were biased to yield higher concentrations. When monochromatic light was led through the unprepared sample, the light was indeed scattered. It is very likely that this turbidity has caused the false high values for nitrate, ammonia/ammonium and phosphorus concentrations. Therefore the total N and total P levels were used in subsequent experiments.
Composition of control group
As stated two control groups were used. The control group ‘complete’ tested the capacity of the used hydroponic set-up to produce cucumber. The nutrient solution supplied to this group contained all essential macro and micro nutrients. The control group ‘adjusted N & P levels’ tested whether the lack of nitrogen and phosphorous nutrients affects plant growth. The composition of the media are stated in table 3 below. Nutrients were added as salts to the water before supplying the water to the plants. K and Ca levels of the ‘adjusted N & P’ group were adjusted for using tap water, the ‘complete’ group nutrients have been dissolved in purified water.
Control group 'complete' Control group 'adjusted N & P'
Species
Amount (g/L)
Species
Amount (g/L)
ammonium nitrate
38.78
ammonium nitrate
1.46
potassium nitraat 33.73 potassium carbonate 45.41 calcium chloride dihydrate
73.36
calcium chloride dihydrate
57.22
potassium dihydrogen phosphate
13.62
potassium phosphate
12.87
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potassium phosphate
28.52
potassium sulphate
28.52
magnesium sulphate
29.29
magnesium acetate tetrahydrate
42.35
di-sodium tetraborate tetrahydrate
1.76
di-sodium tetraborate tetrahydrate
1.76
Tenso YARA Fe-EDDHMA (6% Fe)
4.17
Tenso YARA Fe-EDDHMA (6% Fe)
4.17
Manganese II nitrate tetrahydrate
0.23
Manganese (II) nitrate tetrahydrate
0.23
zinc sulphate heptahydrate
0.02
zinc sulphate heptahydrate
0.02
Copper(II) chloride dihydrate 0.0054 copper(II) chloride dihydrate 0.0054 ammonium heptamolybdate
0.0018
ammonium heptamolybdate
0.0018
Figure 5: The nutrient composition of control group 1 (complete) and control group 2 (adjusted).
Adjustment of dishwater
From the chemical analysis was found that the pH levels were too high to sustain plant growth. Therefore 2M sulfuric acid was added to neutralize. Because of the buffering capacity of several components of the dishwater, exact amounts could not be calculated. A titration has been performed with a 1:11 dilution of the 2M sulphuric acid. 50 ml dishwater with pH 10,67 had to titrated with 0,9 ml of diluted sulphuric acid to reach a pH of 6,50. This means that sulphate concentrations in the dishwater were heightened by 0,15 mM SO3- upon acidifying.
Removal of nutrients from dishwater
To see what the efficiency is of the taking up of nutrients from the dishwater by the cucumber plants, samples were taken before and after the dishwater entered the WWPS. It must be said that this method will give an indication of the nutrient removal rather than the the nutrient uptake by the plants, because nutrients can be lost to the atmosphere by denitrification or be incorporated in biomass which can stick to the substrate. An external party analysed the samples for NH4, NO3, Ntot, Dissolved organic nitrogen (DON), PO4 and Cl. Because of the complexity of the samples, very high PO4 levels, high SO4 levels, relatively high salinity, high turbidity, presence of fats and lots of unknown chemicals, the samples proved very difficult to analyze. One set of samples from before and after entering the WWPS could be analyzed to yield satisfactory results.
Social Methodology
Consumer Acceptance
In order to assess the social willingness of consumers to adapt to the wastewater plant system, a quantitative social research is done. As the research area the Science Park canteen is chosen. Here, possible consumers were interviewed with the use of a cross-sectional research design. Because people from the same scientific discipline might have a bias towards the adaptation to the wastewater plant system, an equal distribution of consumers are selected from the disciplines. The interviews were face-to-face interviews so to avoid the problem of non-response. A risk of this method is that the answers may be biased because the respondents were more like to adjust their answers towards their interviewer. First the general and then the specific questions were asked in order to avoid the order-effect.
The chosen research design has its advantages as well as its disadvantages. Especially during the quantitative research there is little room for digression which makes small differences between respondents hard to show. In other words: the ecological validity is in jeopardy because of the disruption
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of the “natural habitat’’ (Bryman, 2008). But this very same quantitative research has a high replicability, for it can be repeated easily and will probably have the same sort of outcomes. (Bryman, 2008). Consumers were asked about 1) their attitude towards recycling in general 2) their attitude towards the WWPS 3) the possible barriers between intention and actual behaviour. The results of this quantitative questionnaire were analysed with the help of the theory of reasoned action. With the results possible barriers between intentions of behaviour and actual behaviour were identified. These findings can be used to adjust the wastewater plant system, to enhance social acceptance from consumers.
Producer Acceptance
In order to assess the willingness of the producers to adapt and implement the wastewater plant system a qualitative social research is done. In order to gain information about the possibilities for the implementation of the WWSP, a qualitative interview with the operational manager and the location manager was conducted. This qualitative social research consisted of semi-structured open interview. The interview took an hour in which first general questions about reuse were asked and secondly questions about the willingness of Eurest to adjust their detergent in favour of the WWPS as well as their actual willingness to implementation the WWSP. This chosen research design has its advantages as well as its disadvantages. During qualitative research there is room for digression and one can observe small differences between respondents. This makes the observations more realistic; they do not need to be quantified. This means that ecological validity is high, because there is little disturbance of the natural world (Bryman, 2008). The advantage of flexibility during qualitative research is at the same time its disadvantage; replicability is in danger when there is digression from the standard questions. The results of this qualitative questionnaire were analysed with the help of the theory of reasoned action. Possible barriers between producer intention and producers behaviour were identified with the help of the results.
Results
In this chapter the results of both the experimental set-up as well as the social research will be presented.
Potential consumer interview
To get a better understanding of the social acceptance of the wastewater plant system, a series of short interviews were conducted among students of Science Park. In the course of half a day 20 students were targeted for an interview. The interviews were conducted in the mess-hall next to the Eurest canteen. Most people interviewed were actually consuming something bought from Eurest. This means that the people targeted are possible consumers of the cucumbers grown with the wastewater plant system.
Consumer interview part one
First they were asked about their general feeling towards recycling of products and other general reuse of items. Two out of twenty students stated that they had never thought about it, all the others stated that they were positive about the recycling and reuse of products, but when asked about actual behaviour,
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eight respondents stated that they were not active on the level of recycling. This difference is quite interesting, because you would expect someone who thinks recycling is important, to actually do something with recycling themselves. Clearly there must be some barriers between their intentions and their actual behaviour. The diagram below gives an overview of the answers stated during the first part of the interview.
Figure 6: Results first part consumer interview.
Consumer interview part two
The second part of the interview was about the actual wastewater plant system and the attitude of potential consumers towards this system. Their willingness to eat cucumbers grown within the system was researched. Out of the twenty consumers interviewed, nineteen stated that they were willing to eat the cucumbers, but most of them had some extra criteria. These criteria often consisted out of security checks, which should rule out risks involved with eating cucumbers grown on wastewater. Twelve of the respondents stated that they wanted the cucumbers to be tested by an independent agency for certain criteria. These agencies should test the cucumbers in an unbiased way and provide certainty. Also four of the respondents stated that the government should always check the safety of food. It is interesting to see the difference between the amount of people mentioning an independent agency in comparison with the amount of people mentioning a governmental agency. No in-depth interviews were conducted to unearth possible reasons of this difference, but still it is something notable to mention.
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Figure 7: Results second part consumer interview; willingness.
Consumer interview part three
The third part of the consumer interview was designed to uncover possible barriers between the attitude towards the wastewater plant system and the action of actually eating something from the wastewater plant system. In the interview we asked what consumers deemed necessary to eat the cucumbers grown within the wastewater plant system. The most mentioned requirement was the safety of the cucumber. Nineteen out of twenty people mentioned that they would doubt if the cucumbers were safe to eat, and that this was a necessity. The second most mentioned requirement was taste; eight out of twenty people stated that they did not want the cucumbers to taste differently from normal cucumbers, but twelve out of twenty respondents mentioned that they would not mind the cucumbers to taste differently, as long as they were safe. The least mentioned barrier was the cost of the cucumbers. Only one person mentioned that the price of the cucumbers had to be the same as conventional cucumbers for him to eat them. The other nineteen stated that a small difference was not too big of a barrier.
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Figure 8: Results third part consumer interview; barriers.
Producer interview
In general the managers were positive about reuse. However on a private scale the managers of Eurest were not willing to make extra effort for it. On the business level the managers had a positive attitude towards reuse, although they sometimes found it to be cumbersome, because according to them, the circumstances differ per location and therefore solutions concerning reuse cannot be generalized.
Overall the managers were willing to change their detergent in favour of the WWPS, although the actual change is difficult because the supplier of the washing equipment is also the supplier of the detergent. Switching to another detergent would be possible whenever the right detergent is available in the assortment of the supplier. Otherwise the switch would be too expensive. In case of the implementation of the Waste Water Plant System as well as for the selling of the vegetables from this system at Science Park, the managers were overall positive. The system would actually add to the overall experience of Eurest because of the cooperation between the students and Eurest which the system would bring about. Also the positive image this system possibly could provide was seen as a perk. The barriers that were named relate primarily to regulations from above and the costs this system would entail. However, there is sufficient motivation to overcome these barriers which can lead to action such as writing a special policy regarding the Waste Water Plant System.
Plant analysis
The cucumber plants were analyzed by measuring their height above ground and their appearance two times a week. In order to draw conclusions about the dishwater, the growth trend of the cucumber plants on dishwater can be compared to the control groups. The program Matlab 2012b was used for the statistical analysis and for the visualization of the results in graphs. Space delimited files were used as input of the program in the format of text files.18
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Figure 9: Cucumber growth along an age gradient Figure 9 shows the stem length of the plants along an age gradient. The blue line represents the growth of the plants that grew on the regular fertilizer solution (Hoagland’s solution), the green line represents the growth of plants with the adjusted Hoagland’s solution (with the P and N levels of the waste water), the red line represents the growth of the plants that grew on the waste water. It becomes apparent that the hydroponics system worked well, since the plants on the fertilizers solution grew well. The plants with less P and N grew less fast, but were still able to follow a healthy curve. However the plants on the wastewater did not grow sufficiently, in the first days they did grow slightly, but significantly less than the control groups. After 5 days the plants started to wither and died. Even though the control groups were able to grow well on the hydroponics system, the wastewater plants were not able to survive on the waste water. The control group and the test group are subjected to different treatments, therefore independency exists between both groups. A two-sample t-test was conducted to compare the data between the grey water treatment and tap water treatment. Testing at a 0.05 significance level, for H0: equal means between the samples of the control group and the samples of the test group, and Ha: unequal means between the samples of the control group and the test group. The outcome of the two sampled t-test shows that the grey water group differs significantly from control group 1, at a significance level of p=0.0014. This leads to a rejection of the H0 of equal means. Also, the H0 of equal means for the grey water group and control group 2 is rejected at a high significance, with p=0.0062. So, one could conclude that the cucumbers grown with waste water significantly differ from both control groups. This would lead to a conclusion that the grey water group failed during this experiment.
Nutrient removal
Below are the results of the analysis of dishwater samples before entering the WWPS (2 samples) and after entering the WWPS (1 sample).Sample
pH
EC (
μS)
NH4 (μmol/L)
NO3(μmol/L)
Ntot(μmol/L)
DON(μmol/L)
(PO4μmol/L)
Cl (μmol/L)
Before entering 1 10,67 1435 42,8 86,9 776,9 776,9 86,4 1394,3 After entering 1 8,02 1370 <10 3 441,9 441,9 113,7 1358,6 Before entering 2 10,62 1642 70,3 88 1244,9 1244,9 160 1574,8
