Sludge & Waste Management

Biosolids to Market: A Strategic Proposal to Explore the Threats to Biosolids to Land – Now and in the Future

Ref: 18/SL/01/9            Price: £10

ISBN: 1 84057 864 5

Biosolids are valuable sources of crop nutrients, stable organic matter and lime which improve soil quality and fertility. Their recycling to land also completes natural nutrient and carbon cycles. However, there is increasing concern about the fate of substances in biosolids (e.g. microplastics, fibres and organic chemicals) following application to land and their impact on the environment and human health. 
A robust, evidenced based approach to address these emerging issues is required to ensure that biosolids are managed safely and sustainably. 
A comprehensive review of the industry’s approach to biosolids management, and the range of substances/issues that could be present, and which could affect the current practice of biosolids recycling to agricultural land in particular, has therefore been undertaken.

Biosolids: Soil Quality and Fertility Benefits

Ref: 15/SL/01/8            Price: £10

ISBN: 1 84057 780 0

Biosolids are a valuable source of available plant nutrients and stable organic matter, which can reduce manufactured fertiliser costs and benefit soil structure and fertility. This study investigated the effects of twenty years of repeated biosolids applications at four experimental sites.

Soil samples from the sites were analysed for a range of soil chemical, biological and physical properties; measurement of serial crop yields and quality were also made. The report provides scientifically robust experimental evidence on the benefits of long-term biosolids applications to soil quality and fertility and to the nutrient supply to crops.

The results of the study provide information on the benefits of biosolids use, further helping to secure the agricultural landbank for biosolids recycling.

Investigation of the Impact of Historic Biosolids Applications on Soil Microbial Activity

Ref: 12/SL/01/7            Price: £10

ISBN: 1 84057 624 3

This project measured soil microbial properties at sites which had a history of operational biosolids additions in comparison with nearby 'control' fields. It found no statistical differences in soil microbial biomass (a measure of the size of the microbial community) levels between the fields receiving biosolids appications and the 'control' fields, and very few relationships between biomass size and soil heavy metal concentrations. Clover Rhizobium numbers were statistically lower (around 1log₁₀) in the biosolids treated fields than in the 'control' fields, with some inverse relationships between Rhizobium numbers and soil heavy metal concentrations. However, Rhizobium were present in all of the 38 fields sampled to support clover inoculation and growth.

Effects of Sewage Sludge Applications to Agricultural Soils on Soil Microbial Activity and the Implications for Agricultural Productivity and Long-Term Soil Fertility: Phase III

Ref: 08/SL/01/6            Price: £10

ISBN: 1 84057 473 9

Sewage Sludge Applications to Agricultural Soils.

This interim report summarises the results to date from a long-term study evaluating the effects of sewage sludge applications to agricultural soils on soil quality and fertility at nine sites in Britain. The work involved investigating the effects of established soil heavy metal concentrations (i.e. Zn, Cu and Cd) on soil microbial activity and fertility.

In Phase I of the project, metal dose-response treatments were established using selected sludge cakes that contained elevated metal concentrations (i.e. c.6,000 mg/kg Zn; c.5,000 mg/kg Cu; c.44mg/kg Cd) and were applied over a 4-year period (1994-1997), which provided a high-level of 'stress' to the soil microbial community. The sludge cakes were applied to achieve a range of soil metal concentrations from background levels to above statutory soil metal limit values.

Additionally, at three sites in England, the effects of Zn, Cu and Cd additions in the metal-rich sludge cakes were compared with those in metal-amended liquid sludge applications, to provide a contrast in the form of metals applied and organic matter loading rates. The metal-amended liquid sludge treatments were expected to represent 'worst-case' treatments in terms of likely metal availabilities, akin to a long-term situation where organic matter levels had declined and stabilised after sludge application.

Three key soil micrbial properties were measured, viz.: (i) soil respiration rate, a measurement of soil microbial activity (ii) soil microbial biomass carbon (C), a measurement of the total soil microbial population and (iii) clover rhizobia numbers, a specific species responsible for nitrogen fixation. Significant (P < 0.05) responses in soil microbial properties (i.e. rhizobia numbers and microbial biomass size) and agricultural crop quality (i.e. grain Cd concentrations) were measured. Sewage Sludge Applications to Agricultural Soils.

Effects of Sewage Sludge Applications to Agricultural Soils on Soil Microbial Activity and the Implications for Agricultural Productivity and Long Term Soil Fertility

Ref: 03/SL/01/4            Price: £10

ISBN: 1-84057-317-1

This interim report summarises a long term study to date of specific heavy metal ( Zn, Cd & Cu derived from sewage sludges) upon soil microbial diversity and crop uptake. The evidence to date shows that the trials as originally envisaged are establishing well and that existing limit levels in soils appear to be at approximately the right level. Precise data will hopefully result from the next four seasons' trial work.

Exploring attitudes and perceived barriers to the use / recycling of biodegradable products containing sewage sludge

Ref: 15/SL/13/5            Price: £10

ISBN: 1 84057 796 7

Sewage sludge is one of a number of biodegradable organic wastes produced in significant quantities in the UK. These wastes contain valuable nutrients and as a result, products derived from these materials are widely used as fertilisers and soil improvers for assisting plant growth. However, there are barriers to combining and treating sewage sludge with other organic materials to produce biodegradable products containing sewage sludge (BiPS).

The aims of this project were to identify and understand the barriers to the use of BiPS by investigating BiPS products and markets available around the world, their associated hazards and risks and how these have influenced the development of relevant regulations and standards. Perceptions are a very important factor in determining how BiPS is used so the project also sought to understand the perceptions and attitudes to the management and use of BiPS of key stakeholders as well as the general public.

To address the barriers to the use of BiPS in the UK the water industry needs to work closely with stakeholders to explore how to change the regulatory landscape, possibly by establishing product quality standards for different end uses, underpinned by ongoing research into potential hazards in order to provide widespread confidence. The public is generally unaware of the use of sewage sludge and BiPS and further research is required to provide a better understanding of the extent and strength of their views.

Determining Energy Yield from Various Co-digestible Wastes

Ref: 11/SL/13/4            Price: £10

ISBN: 1 84057 601 4

WaSCs are currently uncertain about how to progress co-digestion schemes because of doubts over waste availability, gas yield and allowable business models.
This work screened a large number of potential organic wastes and then carried out a more detailed laboratory study on the digestibility of animal by-product residues, fat-trap materials, food wastes and green wastes. The results are presented in the report.
A competitive 'market' is developing for organic wastes and any gate fee available will vary both geographically and in the nature of the waste involved. Co-digestion making use of existing assets has the potential to provide a low capital cost, environmentally sound recycling route.
Ofwat is currently developing its policy on co-digestion and similar achemes and WaSCs need, for now, to discuss options for individual schemes with the regulator. These potential options are discussed in the report.

Uses for CO2 in Biogas Produced from Anaerobic Digestion - Summary Report

Ref: 11/SL/13/2            Price: £10

ISBN: 1 84057 593 X

The CO2 content of the biogas produced during wastewater treatment is not counted as emissions under normal carbon accounting rules. A key objective of this project was to identify methods for capturing, separating and using CO2 from biogas. The methods identified are based on established technologies used for the upgrading of biogas. A wide range of offsite and onsite uses for CO2 was identified, with a low or negative market value for CO2, whilst onsite uses were more cost effective than the offsite uses.
Another objective was to understand how much the industry can reduce its carbon footprint. The main sources of CO2 emission; sludge incineration, biogas generation, the post-combustion of biogas and the biogenic emission of CO2 from aerobic treatment, account for almost 40% of the total CO2 emissions from the industry. The findings of this project will assist decision making in targeting efforts to mitigate CO2 emissions.
Sold as a set with 11/SL/13/3 (attached on CD).

Sewage Sludge: A Fuel or a Waste?

Ref: 04/SL/13/1            Price: £10

ISBN: 1-84057-338-4

An appraisal of the policy, technological, environmental and social impacts associated with the co-combustion of sewage sludge is presented. Five scenarios for co-combustion were selected to reflect a range of operational scales, project structures and growth potential. These scenarios were subject to thermodynamic and materials flow modelling and were discussed with key stakeholders. The scenarios that can be most rapidly implemented (co-combustion with the power and industrial sectors) are those suffering poor water service provider control and public perception, while those with potentially greater security (co-combustion with wastes or biomass) and sustainability require a greater investment and present significant risks to the water service providers.

Sewage Sludge Incineration

Ref: 01/SL/07/1            Price: £10

ISBN: 1 84057 227 2

The project reviewed sewage sludge incinerator (SSI) design standards and plant performance with respect to Nox and particulate emissions. The report concludes that achievement of Nox standards required by the proposed EU standard will be problematic for some UK SSIs. The project reviewed SSI ash quality and reuse potential. The report concludes that the ash from particulate removal should not be considered special waste. The report concludes that whilst ash recycling is feasible the market is limited and that financial incentives may be required.

Biosolids: Good Practice Guidance

Ref: 14/SL/11/7            Price: £10

ISBN: 1 84057 730 4

This biosolids good practice guidance document is intended to provide advice and information to knowledgeable practitioners on sustainable biosolids recycling to agricultural land. The guide covers the treatment of sewage sludge to produce biosolids, the benefits associated with using biosolids in agriculture and regulatory requirements.
Following the guidance in this document will help practitioners get the most from biosolids applications to agricultural land. From a water industry perspective, the good practice guidance developed in this project will enable operators to secure a sustainable landbank and 'recover' more value from biosolids sales; helping to offset treatment, transportation and application costs.

Sustainable Sludge Thickening and Treatment at Small WwTWs

Ref: 13/SL/11/6            Price: £10

ISBN: 1 84057 671 5

At present, it is usual for thin sludge produced at smaller wastewater treatment works (WwTW) to receive very little treatment before being tankered to a larger WwTW for further treatment. Thus, large volumes of sludge are transported substantial distances. This is expensive and increases the overall carbon footprint of wastewater treatment.

This study investigates alternative approaches for the management of sludge produced at small WwTWs (defined as serving 25,000 population equivalent or less) which may help reduce water company costs and environmental impacts. It considers the overall technical advantages and constraints for these alternatives and provides a comparison of both relative costs (whole life costs and payback periods) and potential environmental effects (arising from transport, sludge liquors treatment, odour and greenhouse gas emissions).

The results of the study provide a framework for considering sustainable sludge management options for small WwTWs which covers technical, economic and environmental considerations.

Using sludge from advanced anaerobic digesters to reduce the rate of phosphorous run-off from farm slurry

Ref: 15/SL/02/11            Price: £10

ISBN: 1 84057 795 9

 The water soluble phosphorus (WSP) content of organic materials is directly related to their potential for P transfer in run-off after land application. Biosolids have a lower WSP than livestock slurry and hence a lower risk of P loss in run-off. The addition of biosolids to livestock slurry at an appropriate rate could reduce the WSP content of the resulting mix due to the binding properties of certain biosolids (as a result of iron-Fe, aluminium-Al and calcium-Ca cations).

A series of experiments were undertaken using a range of biosolids products added to cattle slurry at a variety of mixing rates. The experiments showed that mixing biosolids, or in particular clean water sludge, with slurry did decrease the WSP of the slurry/biosolids mix (compared to slurry). Similarly, the PSYCHIC model predicted a reduction in total catchment P losses, following the addition of the mixed organic material, in comparison to separate applications. 

The Agronomic and Environmental Impacts of Phosphorus in Biosolids Applied to Agricultural Land: A Review of UK Research

Ref: 11/SL/02/10            Price: £10

ISBN: 1 84057 595 6

A review of UK research funded over the last 15 years on the potential environmental impacts of phosphorus (P) in biosolids has concluded that biosolids are a valuable, sustainable source of P whose recycling to agricultural land could be expanded in support of sustainable farming, resource protection and provision of ecosystem services. The eutrophication risk associated with biosolid recycling to land is very small provided biosolid types and application rates are matched to minimise P transfer in runoff based on on-site assessment of P loss risk taking account of hydrological connectivity, the degree of soil P saturation and vulnerability to soil erosion.

Phosphorus Lifecycle Management

Ref: 10/SL/02/9            Price: £10

ISBN: 1 84057 570 0

Phosphorus is a major reason why UK rivers are not achieving good status under the Water Framework Directive. However, before potentially expensive measures are implemented, the impact of phosphorus on the ecology must be understood. The first phase of this project reviewed the derivation of the phosphorus standard and its justification. Furthermore, to identify suitable measures, where required, it is necessary to identify the main sources of phosphorus to a water body. A series of spreadsheet models was therefore developed to quantify phosphorus sources to water and the main outcome from the project was a fully operational conceptual lifecycle management tool combining environmental quality (chemistry and ecology) and sustainability (economics and carbon emissions) for a number of possible future scenarios demonstrated for the Wensum catchment; which could form the basis for future river basin planning.

Validation of Guidelines for the Sustainable Application of Phosphorus in Biosolids to Agricultural Soils

Ref: 09/SL/02/8            Price: £10

ISBN: 1 84057 549 2

To help identify environmentally-sustainable practice with respect to phosphorus (P) in biosolids applied to agricultural land, a field study was undertaken to validate provisional laboratory-based guidelines on release of soluble P in land runoff. As found in the laboratory, the risk of P release from biosolid-amended soils is dependent on both soil type and biosolids type. The study confirmed that the degree of soil P saturation is a reliable indicator for guiding sustainable biosolid practice to avoid eutrophication impacts and should be adopted by the industry to maximise the opportunity to recycle a widely-available and valuable natural resource.

Application of Phosphorus in Biosolids to Agricultural Soils

Ref: 07/SL/02/7            Price: £10

ISBN: 1 84057 449 6

Laboratory studies and field assesssments using representative bisolid types from three regions in England were undertaken to develop practical guidelines on the safe application of phosphorus in biosolids to agricultural land without increasing the risk of eutrophication of adjacent watercourses. The guidelines assess the risk of mobilisation of soil and biosolid phosphorus in runoff and erosion, take account of the hydrological connectivity between the field and the watercourse and suggest potential mitigation options where the risk is high.

Application of Phosphorus in Industrial Biosolids Applied to Agricultural Soils - Review

Ref: 05/SL/02/6            Price: £10

ISBN: 1-84057-370-8

This report reviews biosolid phosphorus, processes of phosphorus loss from land, and the range in measures available to control the loss. The factors affecting risk of P loss from agricultural land were considered and a number of potential measures to control P loss were identified, requiring prior identification of high-risk fields for targetting of these options.
Following visits to 3 water companies, a preliminary methodology for assessing the risk of phosphorus loss as a function of the risk of in-field mobilization and the risk of delivery from the field to the watercourse was developed for testing.

The Environmental Impact of Phosphorus from the Agricultural Disposal of Sewage Sludge -Stage 2

Ref: 96/SL/02/3            Price: £10

ISBN: 1 84057 117 9

Progress is reported for the second year of the three year project. Laboratory analysis indicated that phosphorus available may be low for dewatered, composted or dried sludges. Field experiments indicated that phosphorus leachate and run- off from sludged plots was less than that from plots receiving inorganic fertiliser or livestock slurry. Further lysimeter work confirmed that phosphorus losses are negligible from land treated with sewage sludge. Most of the sludge phosphorus applied to land is retained in the topsoil and this may lead to surface run- off.

The Environmental Impact of Phosphorus from the Agricultural Disposal of Sewage Sludge - Stage 1

Ref: 95/SL/02/2            Price: £10

ISBN: 1 84057 072 5

This report describes progress in the first year of the three year project. All the experimental field sites were established and treatments applied. Sixty sludge sources from around the UK were identified for analytical determination of phosphorus bio- availability and trials undertaken to determine phosphorus loss in land run- off. Early results from lysimeter experiments show low phosphorus levels in leachate from sandy soils treated with liquid digested sludge. Historically sludged sites were sampled to determine the extent of phosphorus accumulation at various levels.

The Signficance of Sewage Sludge as a Source of Phosphorus Loss from Agricultural Land to Surface Waters : A Literature Review

Ref: 95/SL/02/1            Price: £10

ISBN: 1 84057 071 7

Sludge applications based on nitrogen requirements may lead to an accumulation of phosphorus in soil. There is a risk of consequential eutrophication in vulnerable areas. Although the immediate availability of phosphorus from sewage sludge may be low it is considered a useful source to crops in rotations. P loss in surface and sub- surface run- off from freshly sludged land is comparable or less than that from other fertilizers, typically less than 1% of phosphorus applied. The continued land application of sludge poses only a small threat to the environment.

Beneficial Effects of Biosolids on Soil Quality and Fertility – Literature Review

Ref: 99/SL/08/1            Price: £10

ISBN: 1 84057 173 X

Application of biosolids, usually at a rate of 250 kg N ha -1 , will typically apply 5- 8 tds ha -1 , equivalent to 2- 4 t OM ha -1 . Regular application of biosolids at this rate will lead to slow but progressive increases in soil OM content. Biosolids OM has been shown to influence a number of soil physical, chemical and biological properties, which in turn have a positive impact on soil quality and fertility. There is a requirement that the soil conditioning and fertiliser replacement value of a range of biosolids including ‘new’ products is evaluated under UK conditions and at appropriate agronomic rates. This, would provide scientifically based information on the agronomic value of biosolids from which advisory and promotional information could be developed.

Beneficial Effects of Biosolids on Soil Quality and Fertility

Ref: 01/SL/08/2            Price: £10

ISBN: 1 84057 216 7

The literature review and field study measurements have demonstrated that repeated biosolids applications have beneficial effects on a range of soil physical (plant available water supply, soil strength and porosity, and water infiltration rates) and chemical (organic matter and plant available nutrient supply) properties, and crop yields and quality.

The Environmental Impact of Phosphorus from the Agricultural Use of Sewage Sludge - Final

Ref: 00/SL/02/5            Price: £10

ISBN: 1 84057 191 8

This project started in 1994 and most of the experimental work finished in 1998. Progress reports on the work have been published over the last five years. The six final reports from the individual experiments are presented here. Experiment 6, which studies the long term cycling of phosphorus when sludge is used agriculturally, is continuing through the 1999 and 2000 growing seasons and a supplementary report on this work will be issued in mid 2001. Reports presented here are *amounts, form and bioavailability of phosphorus in sewage sludge - final report * accumulation and migration of phosphorus in sludge amended soil - final report, * phosphorus leaching from free-draining soils receiving sewage sludge - final report, * phosphorus loss from drained clay soils receiving sewage sludge - final report, *phosphorus loss in surface run-off from sludge amended soil - final report, * phosphorus cycling in soils receiving sewage sludge - final report. In addition a literature review entitled 'the significance

The Environmental Impact of Phosphorus from the Agricultural Disposal of Sewage Sludge - Stage 3

Ref: 97/SL/02/4            Price: £10

ISBN: 1 84057 013 X

Laboratory, lysimeter and field studies continue to show wide variability the potential bioavailability of phosphorus in sewage sludge. Under operational rates of application, losses of phosphorus in run-off from plots receiving sludge were less than from plots receiving other phosphorus amendments. Leaching losses were significant only from land receiving excessive amounts of sludge biosolids.

Integrated Waste Management

Ref: 11/SL/12/2            Price: £10

ISBN: 1 84057 596 4

The objectives of this project were: to understand the impact of competition and increased scrutiny/concern on recycling of biosolids to agriculture due to an increase in other organic materials being considered for recycling in this manner; and to identify the opportunities and restrictions for the water industry in accepting other organic waste streams at Urban Wastewater Treatment Works.
The project concluded that co-digestion had a key role to play in assisting UK plc to meet its challenging targets for landfill diversion, renewable power generation and greenhouse gas reduction. From a water industry perspective, co-digestion has the potential to bring considerable benefits to the business and to its water customer base. However, there are still a number of regulatory issues that need to be resolved before these benefits can be fully realised, namely: clarification on the mechanisms by which co-digestate can be recycled to land; whether co-digestion can be undertaken as part of the appointed or non-appointed business; and, if the latter, the level of any transfer pricing would need to be agreed.
The study has provided valuable underpinning information that will enable the Water Industry to engage in discussions with the financial and environmental regulators, with a view to enabling more widespread engagement in co-digestion in the future, that will benefit UK renewable power (biogas) generation and the recycling of valuable nutrients to agricultural land.

Comparative Environmental Aspects of Available Biosolids Routes

Ref: 01/SL/12/1            Price: £10

ISBN: 1 84057 238 8

This study provides an independent comparison of the environmental consequences resulting from the selection of the more readily available biosolids processes and uses. Biosolids does not always enjoy a positive public image but the situation can be improved by demonstrating that biosolids use or disposal is safe and is based on a sound understanding of environmental implications.

Enteric Pathogen Survival in Sewage Sludge-Amended Agricultural Soil

Ref: 11/SL/06/8            Price: £10

ISBN: 1 84057 604 9

Biosolids represent the solid fraction of sewage and potentially contain a number of human and animal pathogens. This report describes a series of field trials in which sewage sludge that had been subjected to selected treatment methods was land applied and subsequent pathogen survival assessed.
Nymbers of Escherichia coli in biosolids-amended soils decayed to the background population in field soil within 40-60 days of sludge application. E. Coli O157, Listeria and Salmonella all showed significant decay when introduced to two different soil types in inoculated sludge and were undetectable or at background values within 50-150 days following sludge addition. E.coli numbers in unamended soils were highly dynamic and fluctuated between 1and 6 log10 100 g-1 ds during all field trials.
Clostridium and Campylobacter did not decay to a significant extent when introduced to both soils with sludge.
Sludge application consistently increased protozoa numbers in field soil, with raw sludge having a larger effect than anaerobically digested sludge, presumably due to greater availability of substrates in the unstabilised sludge. Protozoa numbers in biosolids-amended soils remained between 0.5 and 1 log above those of the control in field soil.
A laboratory incubation study provided evidence for the direct effect of soil protozoa activty and other ecological processes on E.coli decay in sludge-amended soil.

Pathogens in Biosolids - Microbiological Risk Assessment

Ref: 03/SL/06/7            Price: £10

ISBN: 1-84057-294-9

Biosolids represent the solid fraction of sewage and potentially contain a number of human and animal pathogens. This report describes a microbiological risk assessment to quantify the risks to humans from consumption of root crops grown on land to which treated biosolids have been applied in accordance with the Safe Sludge Matrix and the Regulations. The seven pathogens studied were Escherichia coli O157, Cryptosporidium, Giardia, Salmonella, Campylobacter, Listeria monocytogenes and enteroviruses. A number of worst-case assumptions have been made to accommodate lack of data. The predicted risks to the UK population as a whole are remote. Indeed, the highest risk is for Cryptosporidium with one infection in the UK population every 45 years on average. The model shows that the 12 month harvest interval compensates for any increased risks due to inefficient operation of sludge treatment at the works.

Pathogens in Biosolids - The Fate of Pathogens in Sewage Treatment

Ref: 02/SL/06/6            Price: £10

ISBN: 1-84507 2612

This study has evaluated the survival of a number of enteric pathogens added to thickened sewage sludge which was subjected to treatment by a range of processes operated under Code of Practice* conditions. These processes were: mesophilic anaerobic digestion (MAD), pasteurisation followed by MAD, lime stabilisation and composting. The experiments were carried out at bench-scale with additions of Salmonella senftenberg, S. dublin, S. enteriditis, S. typhimurium, Listeria monocytogenes, Campylobacter jejuni, Cryptosporidium parvum and poliovirus with the aim of achieving 106 organisms in the sludge. In addition the numbers of indigenous Escherichia coli were determined, not only in the bench-scale reactors but also at nominated full-scale plants that were operated under Code of Practice conditions; thermal drying was evaluated at full-scale only. Indigenous E. coli were shown to have similar survival properties to the verotoxigenic strain of E. coli O157 and could act as an indicator for this pathogen.

Methods for the Detection and Enumeration of Pathogens in Biosolids

Ref: 00/SL/06/5            Price: £10

ISBN: 1 84057 212 4

A generic method has been developed for the resuscitation, detection and enumeration of bacterial pathogens. This provides a robust and flexible platform for pathogens in model digester systems, and in field trials. New methods for cryptosporidia and viruses have also been developed which are also applicable to such sample types. The methods allow enumeration of the target pathogens to be performed in the presence of high background levels of microorganisms. Although the methods were devised specifically for biosolids, the techniques are applicable to wide variety of organic wastes.

Review and Status of Current Methods for the Detectionof Verocytotoxic Escherichia Coli,Salmonella Enteritidis PT4, Salmonella Typhimurium DT104, Shigella sonnei and Campylobacter Jejuni in treated an

Ref: 98/SL/06/2            Price: £10

ISBN: 1 84057 149 7

No abstract is associated with this report.

The Content and Fertilizer Value of Sulphur and Magnesium in Sewage Sludge

Ref: 97/SL/06/1            Price: £10

ISBN: 1 84057 012 1

Reviews the published data on the content and plant availability of sulphur and magnesium in sewage sludge. Surveys sludge samples from 61 centres in the UK on their sulphur and magnesium content, discusses the results and compares these sludges with animal manures. Recommends where future research effort should be concentrated.

E. coli in U. K. Mesophilic Anaerobically Digested Sludges

Ref: 99/SL/06/4            Price: £10

ISBN: 1 84057 170 5

The results of a repeat survey carried out at five operational sites confirm that Mesophilic Anaerobic Digestion can reduce numbers of E. coli by up to 4 orders of magnitude. The average log reduction recorded in the second survey was 2.08, higher than observed in the first survey. 92% of reductions were 2 or greater, compared to 76% in the first survey. This was not unexpected, since the sites had been chosen as among the apparently better sites originally surveyed. Average reductions at the sites varied between 1.35 and 3.36, but there were no clear reasons for the differences.

A Survey of E. coli in UK Sludges

Ref: 99/SL/06/3            Price: £10

ISBN: 1 84057 168 3

A survey was undertaken to rapidly assess the effects of different processes on numbers of Escherichia coli in sludges from all parts the U. K All of the processes surveyed reduced the numbers of E. coli . Composting, lime addition and thermal drying reduced numbers to the limit of detection. 90% of reductions were log 6 or greater. Lagooning of sludge was capable of reductions in the order of log 5 Mesophilic Anaerobic Digestion (MAD), the most popular process in the survey, reduced E. coli by, on average, between log 1.4 and 2.3. The one vermiculture site showed results intermediate between MAD and the “advanced” processes.

Polynuclear Aromatic Hydrocarbons in Sewage Sludge Amended Soil-Crop Systems

Ref: 03/SL/04/3            Price: £10

ISBN: 1-84057-316-3

Sewage sludges can contain organic chemicals from a variety of sources at low concentrations. A previous report ( 02/SL/04/2 ) concluded that polynuclear aromatic hydrocarbons (PAHs) do not accumulate in the terrestrial foodchain and that a proposed EC limit value appears inappropriate. This report describes a study to address the issue. Worst case scenarios of sewage sludge being applied to the surface of grassland were investigated. Pot trials were also conducted with carrots and lettuce to investigate realistic or elevated sewage sludge application rates. The outcome of these studies was that typical UK sludges contain PAH concentrations above the suggested limits, precluding them from agricultural use. Evidence from this work suggests that the sludges pose no risk to the environment, animal or human health when applied under suitably controlled conditions.

Organic Contaminants in Sewage Sludge Applied to Agricultural Land

Ref: 02/SL/04/2            Price: £10

ISBN: 1-84057-277-9

Sewage sludges contain organic chemical contaminants from a variety of sources and at low concentrations. The European Union has proposed that limit values, relating to the application of sewage sludge to agricultural land, are established for some specific classes of compounds. This report presents a critical evaluation of the proposed EU limit values, examining how and why the standards have been derived, considering whether they are scientifically defensible, and the practical implications of trying to implement them. It is shown that the derivation of the proposed limit values has little scientific credibility. Further, it is shown that if the proposed limits are adopted for some chemical classes, the 'sludge-to-land' outlet will be seriously impacted, with little or no benefit to the quality of soils, crops and human exposure to the chemicals in question. The report presents a logical, step-wise approach for considering the fate, behaviour and significance of organic chemical contaminants in sludge-soil-foodchain transfer scenarios, which can be used to help derive scientifically defensible limits.

Pentachlorophenol (PCP) and chloranil as sources of PCDD/ Fs to sewage sludge and sludge amended agricultural soils

Ref: 97/SL/04/1            Price: £10

ISBN: 1 84057

The contribution of pentachlorophenol (PCP) and chloranil- based dyes and pigments to the dioxin (PCDD/ F) content of sewage sludges and the potential for PCDD/ Fs derived from these sources to persist in sludge amended soils and to trtansfer through the agricultural food chain is discussed. Sources, production and use of PCP and chloranil are described along with regulatory issues. Where possible, UK production, use and import statistics have been updated. The application of other types of organic amendments (eg farmyard manure), paper waste sludge and textile waste could represent important sources of PCDD/ Fs to agricultural soils. At present the application of these wastes is not subject to the same level of control as sewage sludge. There is very limited data available at present to quantify their current and future impact. Using a congener- specific pathways analysis model, the addition of sludge containing high concentrations of PCDD/ F congeners associated with PCP and chloranil- based sources does n

Identification of Priority Organic Contaminants in Sewage Sludge Volume 1 containing the main report

Ref: 96/SL/03/1            Price: £10

ISBN: 1 84057 102 0

A review of the occurrence of organic compounds in sewage sludge is presented, with literature compiled on over 300 organic compounds. Likely inputs of organic contaminants to agricultural soils via sewage sludge are determined and results compared against soil quality standards. A screening approach is developed, based on compound physicochemical properties, to assess the likely behaviour and fate of chemicals introduced into agricultural soils in sewage sludge. The propensity for compounds to leach to groundwater or transfer to crop plants and grazing animals is assessed. The sludge- soil/ herbage- livestock' pathway is the most important with regard to potential human exposure of sludge- derived organics. Routine operational practice for the application of sewage sludge to land is very unlikely to result in UK soil quality limits for trace organics being exceeded. Repeated applications of sludge to pasture land may lead to the exceedence of the more stringent soil quality guidelines adopted elsewhere

Survey of PCDD/ Fs and Non- Ortho PCBs in UK Sewage Sludges

Ref: 01/SL/03/4            Price: £10

ISBN: 1 84057 221 3

A survey of the PCDD/ F and non- ortho PCB content in the digested sludge of 14 UK wastewater treatment works was carried out. The range of total PCDD/ F concentration in the sludges was 8880- 428000 pg/ g dw. Total non- ortho PCB concentrations were in the range 272- 63000 pg/ g dw. The PCDD/ F I- TEQs of the sludges studied were comparable to those published in the literature with a range of 20- 225 pg I- TEQ/ g dw. The non- ortho PCBs usually added 3- 4 pg/ g to the total I- TEQ. The homologue group pattern of the PCDD/ Fs was consistent with that found in most sewage sludges.

Recycling of Water Treatment Works Sludges

Ref: 99/SL/09/1            Price: £10

ISBN: 1 84057 167 5

The project assessed the suitability for recycling of water treatment works (WTW) sludges currently produced and recommends actions and changes needed to optimise and secure recycling opportunities. The study comprised the following major elements: 1 a survey of arisings of WTW sludge, disposal costs and current waste management methods 2 a review of legislation and statutory guidance 3 consultation to identify current initiatives for the beneficial use of WTW sludges 4 classification of WTW sludge in terms of suitability for the waste management options identified