Sewage sludge application as a vehicle for microplastics in eastern Spanish agricultural soils
Berg, Pim van den; Huerta-Lwanga, Esperanza ; Corradini, Fabio ; Geissen, Violette - \ 2020
Environmental Pollution 261 (2020). - ISSN 0269-7491
Agricultural soils - Microplastics - Sewage sludge
Microplastic pollution is becoming a major challenge with the growing use of plastic. In recent years, research about microplastic pollution in the environment has become a field of study with increased interest, with ever expanding findings on sources, sinks and pathways of microplastics. Wastewater treatment plants effectively remove microplastics from wastewater and concentrate them in sewage sludge which is often used to fertilise agricultural fields. Despite this, quantification of microplastic pollution in agricultural fields through the application of sewage sludge is largely unknown. In light of this issue, four wastewater treatment plants and 16 agricultural fields (0–8 sewage sludge applications of 20–22 tons ha−1 per application), located in the east of Spain, were sampled. Microplastics were extracted using a floatation and filtration method, making a distinction between light density microplastics (ρ < 1 g cm−3) and heavy density microplastics (ρ > 1 g cm−3). Sewage sludge, on average, had a light density plastic load of 18,000 ± 15,940 microplastics kg−1 and a heavy density plastic load of 32,070 ± 19,080 microplastics kg−1. Soils without addition of sewage sludge had an average light density plastic load of 930 ± 740 microplastics kg−1 and a heavy density plastic load of 1100 ± 570 microplastics kg−1. Soils with addition of sewage sludge had an average light density plastic load of 2130 ± 950 microplastics kg−1 and a heavy density plastic load of 3060 ± 1680 microplastics kg−1. On average, soils’ plastic loads increased by 280 light density microplastics kg−1 and 430 heavy density microplastics kg−1 with each successive application of sewage sludge, indicating that sewage sludge application results in accumulation of microplastics in agricultural soils. Microplastics concentrations in soils are highly proportional to the number of sludge applications.
Phosphorus recovered from human excreta: A socio-ecological-technical approach to phosphorus recycling
Kooij, S. van der; Vliet, B.J.M. van; Stomph, T.J. ; Sutton, N.B. ; Anten, N.P.R. ; Hoffland, E. - \ 2020
Resources, Conservation and Recycling 157 (2020). - ISSN 0921-3449 - 11 p.
Phosphorus recycling - Sewage sludge - Source-separated urine - Struvite - Circular economy - Socio-ecological-technical approach
This article provides a comprehensive and cross-disciplinary overview of the phosphorus cycle through the wastewater and agri-food system. While mineral phosphorus stocks are finite, the use of mined phosphorus is accompanied with many losses, leading to pollution of water bodies. Recovering phosphorus from human excreta can contribute to more efficient use of phosphorus to ensure its availability for food production in the future. Phosphorous can be recovered through different recovery technologies and consequently used in agriculture via different recycling routes. Each recycling route has its own particularities in terms of interactions with technologies, actors and the environment to bring the recovered phosphorus back into agriculture. In this literature review, we adopt a socio-ecological-technical approach to map three phosphorus-recycling routes, via municipal sewage sludge, struvite recovered from municipal wastewater and source-separated urine. We firstly show that improvements are still needed in all three routes for achieving high P recovery efficiency, and a combination of these recycling routes are needed to achieve maximum recovery of phosphorus. Second, we identify key issues for each recycling route that currently limit the use of recovered phosphorus in agriculture. We indicate where interaction between disciplines is needed to improve recycling routes and identify gaps in research on how recovered phosphorus accesses agriculture.
Sulfide induced phosphate release from iron phosphates and its potential for phosphate recovery
Wilfert, P. ; Meerdink, J. ; Degaga, B. ; Temmink, H. ; Korving, L. ; Witkamp, G.J. ; Goubitz, K. ; Loosdrecht, M.C.M. van - \ 2020
Water Research 171 (2020). - ISSN 0043-1354
Iron - Phosphate recovery - Sewage sludge - Sulfide
Sulfide is frequently suggested as a tool to release and recover phosphate from iron phosphate rich waste streams, such as sewage sludge, although systematic studies on mechanisms and efficiencies are missing. Batch experiments were conducted with different synthetic iron phosphates (purchased Fe(III)P, Fe(III)P synthesized in the lab and vivianite, Fe(II)3(PO4)2*8H2O), various sewage sludges (with different molar Fe:P ratios) and sewage sludge ash. When sulfide was added to synthetic iron phosphates (molar Fe:S = 1), phosphate release was completed within 1 h with a maximum release of 92% (vivianite), 60% (purchased Fe(III)P) and 76% (synthesized Fe(III)P). In the latter experiment, rebinding of phosphate to Fe(II) decreased net phosphate release to 56%. Prior to the re-precipitation, phosphate release was very efficient (P released/S input) because it was driven by Fe(III) reduction and not by, more sulfide demanding, FeSx formation. This was confirmed in low dose sulfide experiments without significant FeSx formation. Phosphate release from vivianite was very efficient because sulfide reacts directly (1:1) with Fe(II) to form FeSx, without Fe(III) reduction. At the same time vivianite-Fe(II) is as efficient as Fe(III) in binding phosphate. From digested sewage sludge, sulfide dissolved maximally 30% of all phosphate, from the sludge with the highest iron content which was not as high as suggested in earlier studies. Sludge dewaterability (capillary suction test, 0.13 ± 0.015 g2(s2m4)−1) dropped significantly after sulfide addition (0.06 ± 0.004 g2(s2m4)−1). Insignificant net phosphate release (1.5%) was observed from sewage sludge ash. Overall, sulfide can be a useful tool to release and recover phosphate bound to iron from sewage sludge. Drawbacks -deterioration of the dewaterability and a net phosphate release that is lower than expected-need to be investigated.
Farmer perceptions and use of organic waste products as fertilisers – A survey study of potential benefits and barriers
Case, S.D.C. ; Oelofse, M. ; Hou, Y. ; Oenema, O. ; Jensen, L.S. - \ 2017
Agricultural Systems 151 (2017). - ISSN 0308-521X - p. 84 - 95.
Anaerobic digestion - Biosolids - Manure processing - Organic fertiliser - Sewage sludge - Technology adoption
Processing of organic waste can improve its nutrient availability and content, and thereby increases the agricultural value of the waste when used as fertilisers, while contributing to a more bio-based, ‘circular’ economy. It is therefore important to guide future policies on waste management and on the development of industries related to processing of organic wastes from agriculture, industry and households. However, there is a lack of understanding of the decision-making processes underlying the use of processed and unprocessed organic waste-based fertilisers by farmers. We conducted a survey asking farmers in Denmark about their current use of organic fertiliser, their interest in using alternative types in the future, and their perception of most important barriers or advantages to using organic fertilisers. A representative sample of farmers with > 10 ha of land were sent a questionnaire; in total 452 responses (28% response rate) were received. Almost three quarters of respondents (72%) used organic fertiliser, and half of the arable/horticultural farms (without livestock) used unprocessed manures, suggesting significant manure exchange from animal production farms to arable farms in Denmark. Looking forward three years from the time of the survey, respondents did not expect to increase the amount of organic fertiliser they used. However, future interest in using processed manures (PRO) and urban waste-derived fertiliser (URB) was greater than their use at the time of the survey (66% interest vs 19% current use of PRO and 32% vs 9% current use of URB). Anaerobically-digested slurry, acidified slurry, and composted/thermally-dried manure or slurry were products of particular interest. A large percentage (40%) of farmers did not have access to processed forms of organic fertiliser, particularly PRO (35% of respondents). Farm and farmer characteristics such as farming activity, farmer age, farm size, and conventional/organic farming influenced the likelihood of future interest in alternative organic fertilisers. The most important barriers to the use of organic fertiliser identified among respondents were: unpleasant odour for neighbours, uncertainty in nutrient content, and difficulty in planning and use. Improved soil structure was clearly chosen as the most important advantage or reason to use organic fertiliser, followed by low cost to buy or produce, and ease of availability. Danish government policies aim to increase in manure processing (e.g. increasing anaerobic digestion for bioenergy recovery). A mix of industry and government-led measures could potentially increase availability and farmer-use to meet these targets.
Vivianite as an important iron phosphate precipitate in sewage treatment plants
Wilfert, P. ; Mandalidis, A. ; Dugulan, A.I. ; Goubitz, K. ; Korving, L. ; Temmink, H. ; Witkamp, G.J. ; Loosdrecht, M.C.M. Van - \ 2016
Water Research 104 (2016). - ISSN 0043-1354 - p. 449 - 460.
Iron - Mössbauer spectroscopy - Phosphorus - Sewage - Sewage sludge - Vivianite
Iron is an important element for modern sewage treatment, inter alia to remove phosphorus from sewage. However, phosphorus recovery from iron phosphorus containing sewage sludge, without incineration, is not yet economical. We believe, increasing the knowledge about iron-phosphorus speciation in sewage sludge can help to identify new routes for phosphorus recovery. Surplus and digested sludge of two sewage treatment plants was investigated. The plants relied either solely on iron based phosphorus removal or on biological phosphorus removal supported by iron dosing. Mössbauer spectroscopy showed that vivianite and pyrite were the dominating iron compounds in the surplus and anaerobically digested sludge solids in both plants. Mössbauer spectroscopy and XRD suggested that vivianite bound phosphorus made up between 10 and 30% (in the plant relying mainly on biological removal) and between 40 and 50% of total phosphorus (in the plant that relies on iron based phosphorus removal). Furthermore, Mössbauer spectroscopy indicated that none of the samples contained a significant amount of Fe(III), even though aerated treatment stages existed and although besides Fe(II) also Fe(III) was dosed. We hypothesize that chemical/microbial Fe(III) reduction in the treatment lines is relatively quick and triggers vivianite formation. Once formed, vivianite may endure oxygenated treatment zones due to slow oxidation kinetics and due to oxygen diffusion limitations into sludge flocs. These results indicate that vivianite is the major iron phosphorus compound in sewage treatment plants with moderate iron dosing. We hypothesize that vivianite is dominating in most plants where iron is dosed for phosphorus removal which could offer new routes for phosphorus recovery.
Phosphorus recovery from sewage sludge char ash
Atienza-Martínez, M. ; Gea, G. ; Arauzo, J. ; Kersten, Sascha R.A. ; Kootstra, A.M.J. - \ 2014
Biomass and Bioenergy 65 (2014). - ISSN 0961-9534 - p. 42 - 50.
Ash - Char - Phosphorus - Sewage sludge - Thermochemical processing
Phosphorus was recovered from the ash obtained after combustion at different temperatures (600°C, 750°C and 900°C) and after gasification (at 820°C using a mixture of air and steam as fluidising agent) of char from sewage sludge fast pyrolysis carried out at 530°C. Depending on the leaching conditions (extraction time, acid load and acid concentration, and type of acid) 90% mass of the original P was recovered. Regarding char combustion ash, higher phosphorus yields are obtained from ash obtained at 900°C than at 600°C and 750°C when using sulphuric acid. Combustion temperature does not affect phosphorus leaching with oxalic acid. A contact time of 2h and an oxalic acid load of 10kgkg-1 of P seem sufficient for phosphorus extraction. Almost all phosphorus present in gasification ash is leached after 2h with both sulphuric and oxalic acid using an acid load of 14kgkg-1 of P. Char ash is a possible renewable source of phosphorus and it can be an alternative to rock phosphate in fertilizer production. The combination of sewage sludge pyrolysis, combustion or gasification of the char and phosphorus extraction from the final solid residue contributes to the integral exploitation of sewage sludge.
Do elevated soil concentrations of metals affect the diversity and activity of soil invertebrates in the long-term?
Creamer, R.E. ; Rimmer, D.L. ; Black, H.I.J. - \ 2008
Soil Use and Management 24 (2008)1. - ISSN 0266-0032 - p. 37 - 46.
Litterbags - Metals - Sewage sludge - Soil - Soil invertebrates
This study aimed to elucidate the response of diversity and activity of soil invertebrates to elevated soil metal concentrations that were a result of sewage sludge application. Field sampling of soil invertebrates was carried out from 2002 to 2004 at an experimental site established in 1982 to test the effects on crop production of metal contamination from sewage sludge applications with elevated concentrations of zinc (Zn), copper (Cu) and nickel (Ni) with certain treatments exceeding the current UK statutory limits for the safe use of sludge on land. At metal concentrations within the limits, none of the invertebrates sampled showed adverse effects on their abundance or overall community diversity (from Shannon-Weiner index). At concentrations above the limits, individual taxa showed sensitivity to different metals, but overall diversity was not affected. Earthworm abundance was significantly reduced at total Cu concentrations at and above 176 mg kg-1, while nematode and enchytraeid abundances were sensitive to Cu and high Zn concentrations. Correspondingly, litter decomposition was lower in Zn and Cu treatments although there was no direct relationship between decomposition and soil invertebrate abundance or diversity. Such enduring changes in both soil biodiversity and biological activity around the current UK regulatory limits warrant further investigation to determine whether they indicate detrimental damage to soil functioning over the long-term.