Using urban mining techniques to capture
phosphorus from agricultural run-off
Will this be possible in an ecologically and economically
sustainable manner?
Verschoor en Omen, 2014
Bart Hoekstra 10645705 Renee Snoek 10761330 Stefan van der Wal 10537252 Course: Interdisciplinary Project Teacher: Anneke ter Schure Expert: Andres Verzijl Word count:
Abstract
Phosphorus is essential to life on Earth and frequently limits the productivity of ecosystems. Nowadays, a substantial portion of the global human population relies on finite phosphate rock resources used for chemical fertilizer production. In order to meet the growing food demand, agricultural land per unit area required to achieve maximum efficiency. Poor management of these resources and continued efforts to enhance soil fertility have stimulated interest in phosphorus recycling and recovery. In the Netherlands agricultural land belongs to the most intensively used land in Europe. Recent studies, however, show the harmful effects of these fertilizers. This research report aims to address useful ‘urban mining’ techniques for recapturing phosphorus.
Content
Introduction Page 3
Research question Page 3
Methods Page 4
Theoretical background Page 4
Analysis of the methods Page 8
Discussion Page 9
Conclusion Page 9
Literature Page 10
Introduction
Agricultural land in The Netherlands belongs to the most intensively used land in Europe. One of the factors enabling such intensive use, is the use of (artificial) fertilisers. Application of these fertilisers provides plants with necessary nutrients (nitrogen, phosphate and potassium), but is not without negative consequences: agricultural run-off from fields often causes eutrophication in both adjacent surface water and distant estuaries. Another issue is the limited supply of these nutrients which are so essential to our welfare. Contrary to nitrogen, which is extracted from the air, phosphate is currently a non-renewable resource, as it is mined, used and then disappears in the environment. Alarmingly, ‘peak phosphorus’ is forecast somewhere in the 2030’s, which can have significant negative effects on the global food supply (Elser & Bennett, 2011). Tilman et al. (2001) projected that the demand for phosphate fertilizer would increase from 3.43 × 107 tons in 2000 to 4.76 × 107 in 2020 and to 8.37 × 107 in 2050. Its rapid consumption is fast diminishing the natural supplies annually (Pastor et al., 2010). In order to have a sustainable supply of phosphorus, recovering these nutrients from agricultural run-off therefore seems imperative. Recovering, or ‘mining’, these nutrients from agricultural run-off can thus have a positive effect on both the ecological status of waterbodies and riparian areas as well as provide us with a constant supply of essential nutrients.
In this research our objective is to identify and analyse the efficiency, impact and feasibility of urban mining techniques with regards to the recovery of nutrients from agricultural run-off. Therefor our research question is: How can urban mining techniques be used to re-use
agricultural run-off in an ecologically and economically sustainable manner in the Netherlands? This requires a thorough interdisciplinary analysis of both hydro-ecological
effects of these solutions as well as an analysis of the economics and factors that can positively influence the viability of related business models. Because of the aforementioned relevance, we focus on the recovery of phosphorous in particular, although other nutrients may be present in (parts of) the feasibility study.
An essential part of this study will be comprised of a comparison between different organizational structures, that could be used by an actor aiming to recapture phosphorous. This will be followed by a feasibility study. Feasibility studies are a tried and tested tool in the implementation of sustainable and socially responsible enterprises and government initiatives (Shen et al., 2010). Each technological process and organizational structure for recapturing agri-runoff phosphorus, will be analysed and its strengths and weakness catalogued.
Research question
How can urban mining techniques be used to re-use phosphorus from agricultural run-off in an ecologically and economically sustainable manner in the Netherlands? Sub questions
1: What is urban mining, which techniques can be used to capture argicultural run-off and on what scale is this already happening?
2: What are the characteristics of phosphorous within runoff, and runoff events? 3: How can the substances found in the agricultural run-off be re-used (what is their value)?
4: How is the discharge of these substances distributed spatially? What kind of urban mining techniques are applicable for capturing them?
5: What kind of viable business model can be used or set-up for re-using the substances?
Methods
The “Urban mining” techniques will be researched through a literature research. Specifically attention will be focused on the efficiency, costs, modes of action (distributed vs. point-based) and impact on the environment (hydro- and ecology) of available technologies. A point-based system has been made to compare and rank different technologies.
Next to find the potential solutions, the techniques, there will also be a literature research on agricultural run-off. In particular the focus will be on the phosphorus content of agricultural run-off and the effects on the surface water quality. Research will also be done on the effect of phosphorus on the environment. E.g. it may have significant downsides in terms of water flow or the migration of fish. In order to do a proper assessment of techniques, such factors need to be taken into account.
The technological processes that could be used to recapture phosphorous vary, therefore the organizational structures that could be used, are similarly varied. It could be that recapturing P is most effectively managed by a private enterprise, or that a joint effort by industry and government actors would be most successful. Therefore this study will examine which structure could be most effective by looking at similar projects completed in the past.
These structures and technological process will then be analysed by means of a feasibility study. Feasibility studies aim to be objective and rational descriptions of the strengths and weaknesses of future endeavours, and ultimately determine the potential success of the proposed endeavour (Justis & Kreigsmann, 1979). The basic concept of a feasibility study is to determine the costs and benefits that are incurred during a certain process. These costs and benefits are found through a detailed description of the operations and management of the process in question, accounting statements, marketing research and policies, financial data, legal requirements, tax obligations, stakeholder issues (ibid) and in this case a look at the process from an ecosystem service perspective.
Literature research into what is possible with urban mining techniques. Literature research into what kind of business model would fit these urban mining techniques.
Another method that will be used includes a feasibility study. This study aims to rationally and objectively uncover the opportunities and threats present in the environment, the strengths and weaknesses of proposed venture, and ultimately the prospects for success. Moreover, in this research two criteria to judge feasibility are value to be attained and cost required.
Theoretical background
In order to determine the economic and ecological feasibility of technological solutions to mine P from agricultural runoff, the nature of runoff first needs to be understood, technologies need to be researched and compared in a standardized fashion, and relevant economical models and factors need to be analysed. In the following section we therefore address the cause and characteristics of runoff, the economics of profitably mining nutrients from run-off and the technologies that are at the core of the concept.
The methods for capturing phosphorus from water
There is a large variety of methods available for capturing or removing phosphorus from water. Within each of the overarching methods there are also multiple techniques available, each with their own advantages and disadvantages. Even within the individual techniques more variety is possible, for example by using different materials to achieve the same process. De-Bashan and Bashan (2004) give an overview of some of the most common ways to remove phosphorus from water. Following here is an overview of the methods they address.
The first overarching method is the precipitation of phosphorus by metal salts. This is a chemical process, which creates a sludge in which the phosphorus can be found, bound to the chemicals from the metal salts. This is the currently most used way to remove phosphorus from wastewater, but it comes with significant downsides, like high cost and an increased sludge production by up to 40 percent (Lenntech, d.u.). There are however options to make it cheaper, one way is by choosing different sources for the materials that are used. It is for example possible to use oyster shells as a source of calcium, which is relatively cheap and also ecologically more attractive because you recycle waste materials (Lee et al., 2009). The second main method that is addressed is the cultivation of microorganisms in wastewater. These microorganisms are divided into two techniques: one uses bacteria and the other uses algae. The example de-Bashan and Bashan (2004) give for bacteria in this case are a species of cyanobacterium called phormidium bohneri. These bacteria grow for two to three days in the water, removing nitrogen and phosphate. Because the bacteria multiply by removing the nutrients they produce biomass, which could potentially be recycled as a fertilizer. A significant problem with the use of bacteria is that they grow very slowly in cold water (around 5 degrees Celcius). This would limit their use in the Netherlands to only the warmer seasons. The algae Asland & Kapdann (2006) and de-Bashan and Bashan (2004) use is a species called Chlorella vulgaris. This species of algae is capable of removing significant amounts of phosphorus from the water, which leads to growth of the algae. Because the algae spread through the water when uncontrolled, measures have to be taken to ensure ease of removal to retrieve the phosphorus. One way to immobilize the algae is to suspend them in two polysaccharide gels. While this does limit their growth it is very effective as a way to be able to remove the algae from the water again (de-Bashan and Bashan, 2004).
The third and final method that De-Bashan and Bashan (2004) discuss in their paper are constructed wetlands. In this method an artificial wetland is created, which can differ in size from something as small as a bucket up to as large as a pond. How effective this method is depends on different factors, like the size, position and material used in the wetland. Xu et al. (2006) tested a number of different materials and showed that the amount of phosphorus each material can absorb varies greatly. The sands tended to perform far poorer than the furnace slag and fly ash. For use in urban mining price and availability also have to be taken into account, so something more in the middle of their tests might be a better choice. Similar soils to those Xu et al. (2006) tested could also be available in the Netherlands, providing enough affordable material to be used in constructed wetlands.
Runoff
Increased fertilisation of crops is one of the key components of the gains in food production of the past century. Application of (artificial) fertilisers has been incredibly successful from the perspective of increased yields, but is not without consequences for the ecological status of ecosystems, specifically quality of surface water. Nitrogen and phosphorous — the latter of which is our focus within this research project — are prone to cause eutrophication and have done so all around the world. In order to alleviate the impact of these nutrients on surface water, both regulatory and technological measures need to be taken to reduce the concentrations of these substances within water ecosystems to acceptable levels.
In our research we aim to find out how urban mining technologies can play a role in reducing the phosphorous-load of surface water. In order to do so it is critical to first understand the physicochemical aspects of P within surface water and agricultural runoff.
Phosphorous speciation
Within the literature, phosphorous is often divided within four categories based on chemical and physical characteristics of the substance. Chemical characteristics are a primary consequence of the method of application: organic P is bound to organic matter and present in
e.g. manure, whereas inorganic P is the ‘pure’ form of mineralised phosphorous applied through e.g. artificial fertilisers. Physical characteristics are the result of the difference in particle size. Particulate P (PP) is generally defined as > 0.45µm in diameter and dissolved P (DP) consists of smaller fractions (Hart, Quin, & Nguyen, 2004). Knowledge on the speciation of phosphorous in runoff is important in order to determine the feasibility of potential solutions, as the efficiency of these solutions, determined by the mode of action of technological solutions, may depend largely on the form of P within the water.
One of the key factors determining the physical speciation of P within runoff is the landscape topography. According to Hart, Quin & Long Nguyen (2004) particulate P appears more predominant in runoff from steep terrain, whereas DP is more predominant in runoff from flatter terrain. This can be explained by a higher degree of soil erosion in steeper terrain. Possibly, although missing in the Hart et al. (2004), a shorter water retention time within steeper landscapes can also explain the relative increase in PP, since there is simply less time for available water to dissolve PP to DP (cf. Heathwaite, Griffiths, & Parkinson, 1998). Unsurprisingly speciation of P is also highly dependent on precipitation and precipitation intensity. Increasing water saturation time relates to a relative increase in DP to PP, which becomes visible when one compares DP-PP ratios on top of a hill with ratios at the foot of a hill. Assuming surface transport along the entire length of the hill, downslope P has had a longer water saturation time and is thus further dissolved than upslope P (Heathwaite et al., 1998). However, this does not necessitate a predominance of DP in wetter periods, as simultaneously increased precipitation also increases soil erosion and erosion susceptibility (also as a result of e.g. cattle grazing), both of which have a positive influence on the PP fraction (Hart et al., 2004).
Runoff events
It was once thought that P was relatively immobile within soils. Farmers were stimulated to increase the bio-availability of P with fertilisers, which was thought to be of little consequence to the environment. However, soils are not P sinks with an unlimited capacity. At one point an equilibrium is reached and additional P applied through fertilisers will not bind to the soil and instead disappear into the environment, either through surface flow or subsurface leaching (Breeuwsma & Silva, 1992; Hart et al., 2004). In agronomic terms runoff of P into surface waters is fairly inconsequential, yet even small concentrations of phosphorous are able to cause significant changes into the environment, specifically eutrophication of (surface) water bodies.
Even though subsurface leaching can be significant, it is established that the primary mode of transport of phosphorous into water bodies is mostly through surface flow (Hart et al., 2004). In both cases precipitation is needed to get the runoff process started. Precipitation intensity, soil erosion (including tillage and grazing) and plant cover are the key factors determining the depth at which water penetrates the top layer of the soil and subsequently determine the scale of P runoff (Smith, Sharpley, & Ahuja, 1993). Vegetation cover generally decreases P runoff, which consequently is lower in forest areas than in pasture and grasslands (Verheyen et al., 2015).
The impact of short-term rainfall events on runoff can be significant. In grassland or forest areas short-term events are relatively inconsequential, whereas within the arable land area, just a few rainfall events contribute significantly to the annual runoff of P: 0.1-0.22 kg P ha-1 in 3-6 events, mostly a result of surface flow after intense precipitation (Verheyen et al., 2015). Similarly Hart et al. (2004) conclude that P runoff peaks right after manure or artificial fertilisers have been applied. This reinforces the idea that a potential technological solution needs to have a sufficient capacity to deal with sudden peak flows of P in surface water. Although examples in literature are scarcely documented and not quantified, it is likely that
tillage causes a spike in P runoff as well. All these factors combined are indicative of the significant influence of short-term runoff-events on the total P export.
Besides surface runoff, subsurface leaching into groundwater— sometimes referred to as a form of runoff— can also play a significant role in total P export from agricultural land. Since none of the technologies we assess within this research deal with groundwater, we do not include this type of ‘runoff’ within our definition.
Cost-effectiveness
The main environmental consequence of agricultural runoff is the potential eutrophication of surface waters. This not only has an environmental cost in terms of degraded ecosystems, but also has an actual economical cost: the cost of environmental degradation affecting economic activity and the cost of cleaning up this ‘pollution’. The former expresses itself in e.g. a decrease in fish stocks, which negatively affects the fishing industry, whereas the latter increases e.g. the costs of water treatment and remediation. To be able to compare actual economic and environmental costs and analyse cost-effectiveness, it is important to have a common term in which these costs are expressed.
Within economics it is increasingly common to try to value the services ecosystems provide to humans. Some of these services directly impact our quality of life, such as food and water provisioning and nutrient cycling. Other services have a more indirect impact on our life, such as biodiversity and even the cultural value ecosystems provide. By expressing the benefits of these services in terms of monetary value, it becomes possible to include the services — or benefits — they provide within a cost-benefit analysis. Consequently, investments can be measured not only in direct costs and benefits, but also in terms of lost or improved quality of ecosystem services (Hanley, Shogren, & White, 2013).
This however requires extensive knowledge of the involved ecosystem services and a definition of the limits, both in terms the spatial extent of the ecosystem as well as a thorough definition of what constitutes these separate services. Knowledge about the tipping points within these spatially constrained ecosystem services is required to be able to estimate the change in ecosystem functioning as a consequence of the assessed investment. Subsequently research needs to be done to determine how much consumers value these services, through e.g. contingent valuation (willingness to pay/accept a change in the functioning of an ecosystem service) or revealed preferences (e.g. comparing the increase of real estate prices close to a park with more distant real estate indicates the value of the park). Unfortunately, none of these factors are easily determined within the scope of this project. We were also unable to find any research containing freshwater ecosystem valuations in The Netherlands. Examples from other countries were found, but cannot be used because contingent valuation and revealed preference valuation can differ significantly from country to country. Therefore we have decided not to use ecosystem valuation within the scope of this project (Hanley et al., 2013).
Instead, we take a simpler approach to measure the cost-effectiveness of technological solutions by: costs abated relative to planned measures to improve surface water quality. A critical component of participation in the European Water Framework Directive is setting policy goals and creating plans to improve water quality. To achieve these goals, the Dutch government has implemented and planned an array of measures. The benefits of the technological solutions we assess can thus be measured relative to these governmental measures. When the solutions are cheaper than the WFD plans, there is a net profit.
Van der Bolt et al. (2008) have assessed the cost-effectiveness of the Dutch WFD plans in three scenarios: 1. a farm-focused scenario where a change in farming practices is aimed at reducing N and P emissions; 2. a parcel-focused scenario in which land plots are optimized to reduce N and P emissions; 3. a ditch-focused scenario that consists of measures to reduce N and P emissions from waterways. They conclude the costs for the reduction of every kg of P
within surface water for the three scenarios are respectively €615, €937 and €435. Rational economic decision-making would therefore favor the third scenario, which will thus be the benchmark in our analysis. Consequently, technological solutions that are more cost-effective than €435/kg are likely to be economically feasible.
Analysis of the methods
As mentioned before several technologies are available for controlling phosphorus pollution. These processes can be classified as chemical methods, (precipitation of phosphorus by metal salts), physical methods (cultivation of microorganisms), and biological methods (constructed wetlands). However, each method represents its own advantages and disadvantages. Nguyen et al. (2014) conclude that the physical method has high chemical expense, effluent
neutralization requirement, and inadequate efficiency for dilute phosphorus solutions. The major concerns using biological removal technologies are complicated operation. In the table below the focus is on the three methods mentioned in the theoretical background paragraph.
1. Precipitation of phosphorus by metal salts 2. Cultivation of microorganisms in wastewater 3. Constructed wetlands Technological
Mode of action Creates a sludge in which the
phosphorus can be found, bound to the chemicals from the metal salts.
Microorganisms grow in the water, taking up the phosphorus.
Soil material in the
constructed wetland absorbs phosphorus from the water.
Efficiency +
Phosphorus removal efficiencies in this process ranged from 75% to 85% (Moriyama et al., 2001). +/- Algae: 78% removal, down to 30% at higher concentrations (Asland & Kapdann, 2006) Bacteria +/- Removing up to 75% of the nutrients in the wastewater (de-Bashan, et al. 2004).
Capacity/Peak capacity
-
All isolates grew well between 15*C and 25* C, growth was limited at 5*C. (de-Bashan and Bashan, 2004). Economics
Initial costs +/- $0.38 per kg P (Huang et al., 2015).
+
Purchase of the algae / bacteria, as well as a container and the gels.
++ / - Construction of the wetland, price depends on size and soil material.
Maintenance In between each
“harvest” very little.
Very little
Discussion
For our research we only looked at three methods for mining phosphorus. However, nowadays there are many more methods available. For future research even broader research might be necessary, as more options become available and affordable. Another point of discussion is about management techniques. These should be included as well. However, in our timeframe this was an impossible option, but nevertheless an important aspect. Direct costs regarding fertilizer production were another problem. These were difficult to find and differ in the literature.
Conclusion
Over the long run, P recycling will become very important to global food security. Nowadays there are more opportunities for the stimulation of innovation in the recycling sector. Recycling and recovery strategies to manage P and source reduction that slow the depletion of finite resources and support the productivity of food systems are needed.
the algae it is easy to remove.
be removed, because the phosphorus is inside it. Source material Oyster shells /
comparable material + metal
Algae / Bacteria Many different choices for the soil material, each with its own efficiency.
Mined product Sludge with precipitated phosphorus.
Biomass with phosphorus inside.
Soil with absorbed phosphorus inside. Implementation Water is mixed with
the metal salt, creating precipitated phosphorus, which can be found in the sludge.
Suspended in two polysaccharide gels.
A wetland is constructed, but the size can vary from as small as a bucket to as large as a pond.
Management factors
Time scale Spent alum sludge adsorbed
phosphorus rapidly, with phosphorus reduced 55% in the first 20 min after exposure (de-Bashan, 2004).
The concentration of P in the effluent decreased from 6.62 to 0.02 mg P L1 after a residence time of 48 h (de-Bashan, 2004).
Depending on the material the sorption capacity can very greatly. The research from Xu et al. (2006) had a maximum lifetime for sand of nine months, while the furnace slag could take up to 22 years before sorption capacity is reached.
Literature
Aslan, S., & Kapdan, I. K. (2006). Batch kinetics of nitrogen and phosphorus removal from synthetic wastewater by algae. Ecological Engineering, 28(1), 64-70.
de-Bashan, L. E., & Bashan, Y. (2004). Recent advances in removing phosphorus from wastewater and its future use as fertilizer (1997–2003). Water Research, 38(19), 4222-4246. Breeuwsma, A., & Silva, S. (1992). Phosphorus Fertilisation and Environmental Effects in
The Netherlands and the Po Region (Italy) (p. 39). Wageningen: DLO The Winand Staring
Centre for Integrated Land, Soil and Water Research.
de-Bashan, L. E., & Bashan, Y. (2004). Recent advances in removing phosphorus from wastewater and its future use as fertilizer (1997–2003). Water Research, 38(19), 4222-4246. Elser, J., & Bennett, E. (2011). Phosphorus cycle: A broken biogeochemical cycle. Nature, 478(7367), 29–31. http://doi.org/10.1038/478029a
Hart, M. R., Quin, B. F., & Nguyen, M. L. (2004). Phosphorus Runoff from Agricultural Land and Direct Fertilizer Effects. Journal of Environment Quality, 33(6), 1954–1972.
Heathwaite, A. L., Griffiths, P., & Parkinson, R. J. (1998). Nitrogen and phosphorus in runoff from grassland with buffer strips following application of fertilizers and manures. Soil Use
and Management, 14(3), 142–148.
Huang, H., Liu, J., & Ding, L. (2015). Recovery of phosphate and ammonia nitrogen from the anaerobic digestion supernatant of activated sludge by chemical precipitation. Journal of Cleaner Production, 102, 437-446.
Lee, C. W., Kwon, H. B., Jeon, H. P., & Koopman, B. (2009). A new recycling material for removing phosphorus from water. Journal of Cleaner Production, 17(7), 683-687.
Lenntech. (d.u.). Phosphorous removal from wastewater. Retrieved 20/11, 2016, from http://www.lenntech.com/phosphorous-removal.htm
McDowell, R. W., Sharpley, A. N., & Condron, L. M. (2001). Processes controlling soil phosphorus release to runoff and implications for agricultural management. Nutrient Cycling
in Agroecosystems, (59).
Moriyama, K., Kojima, T., Minawa, Y., Matsumoto, S. A. T. O. R. U., & Nakamachi, K. A. Z. U. O. (2001). Development of artificial seed crystal for crystallization of calcium phosphate. Environmental technology, 22(11), 1245-1252.
Nguyen, T. A. H., Ngo, H. H., Guo, W. S., Zhang, J., Liang, S., Lee, D. J., ... & Bui, X. T. (2014). Modification of agricultural waste/by-products for enhanced phosphate removal and recovery: Potential and obstacles. Bioresource technology, 169, 750-762.
Shen, J., Yuan, L., Zhang, J., Li, H., Bai, Z., Chen, X., ... & Zhang, F. (2011). Phosphorus dynamics: from soil to plant. Plant physiology, 156(3), 997-1005.
Smith, S. J., Sharpley, A. N., & Ahuja, L. R. (1993). Agricultural Chemical Discharge in Surface-Water Runoff. Journal of Environmental Quality, 22(3), 474–480.
Pastor, L. Mangin, D Ferrer, J. Seco, A (2010). Struvite formation from the supernatants of an anaerobic digestion pilot plan. Bioresour. Technol., 101 (2010), pp. 118–125
D. Tilman, J. Fargione, B. Wolff, C. Antonio, A. Dobson, R. Howarth, D. Schindler, W.H. Schlesinger, D. Simberloff, D. Swackhamer (2001). Forecasting agriculturally driven global environmental change. Science, 292 (2001), pp. 281–284
Xu, D., Xu, J., Wu, J., & Muhammad, A. (2006). Studies on the phosphorus sorption capacity of substrates used in constructed wetland systems. Chemosphere, 63(2), 344-352.
Data Management Table
Discipline or Sub discipline
Name Theory + insights it gives into problem
Key Concepts Underlying
assumptions (ontological, epistemological, methodological, general) 1. Business Cost-benefit analysis Economic impact of nutrient management Markets, costs, transactions, fertilizer prices, future prices.
To what extent will reuse of P be more profitable?
2. Business
Nutrient Use Efficiency Compares the value of nutrients
N and P, management options, reuse op nutrients
Which nutrients are most important and valuable
3.
Business/ Earth Sciences
Material flow analysis Describes several movements of nutrients in water Flow and stocks, material flow analysis, reuse of nutrients To fully incorporate circular systems into economies it is important to integrate the flows and stocks’ societal dimension into the MFA 4. Business ‘Double benefit’ Theory Reusing P and maintaining a healthy ecosystem Combats the destructive impacts of over-fertilization Recovering P, instead of losing it as water pollution 5. Earth Sciences Factors influencing phosphorous speciation in water Primarily dependent on landscape slope and form of P (organic vs. inorganic) Phosphorous speciation, erosion, soil adsorption, runoff Speciation may influence which and how potential recovery technologies are used.
6. Earth Sciences
Event-specific loss of P Heavy precipitation, application of fertiliser and potentially tillage are significant contributors to P loss. In agricultural land most export P occurs in just a few events.
P runoff, event-specific P loss
A large share of total P loss is caused by few specific events, so peak capacity is an important factor to consider in the feasibility study. 7. Earth
Sciences
P leaching
Largely determined by P saturation and soil texture. May export a significant share of P in some sites. Phosphorous leaching, soil texture, P saturation Although generally a minor issue, P leaching can be an important factor to mitigate and take into account when determining feasible technologies. 8. Earth Sciences Impact Primary impact is eutrophication of surface water. Situation in Netherlands has significantly improved between 1980-1996. In Europe livestock
agriculture is the primary cause of water quality deterioration of which 17-26% is caused by P in surface water. Impact, eutrophication Impact of P on surface water is relevant to know in order to determine the locations where impact of technological solutions can be maximized. 9. Earth Sciences Calcium-phosphorus precipitation
The source material, oyster shells, is both ecologically and
economically sustainable.
Oyster shells, economically sustainable
The waste material from oyster shells may not be as available as it is currently in the future. For example through better recycling or another industry that develops a demand for the shells. This would lead to price increases and may make the method no longer sustainable.
