230 results found
Liu J, Smith S, 2020, A multi-level biogas model to optimise the energy balance of full-scale sewage sludge conventional and THP anaerobic digestion, Renewable Energy, Vol: 159, Pages: 756-766, ISSN: 0960-1481
Anaerobic digestion (AD) is a long-established method for treating wastewater sludge and has been extensively researched, but there remains a lack of generic or practical modelling tools to guide operators and maximise the energy output. Detailed kinetic models have been developed, but are too complex as practical tools for industrial level application. A multi-level model of biogas yield (BY) was therefore developed based on operational data from 72 full-scale sites in the UK showing a wide range of AD performance. The model focused on the controllable operational parameters that are currently monitored at full-scale, including: temperature, hydraulic retention time and dry solids content in the feed sludge. The model effectively described performance variations in BY of full-scale processes, and provides a practical management tool to aid decision support to improve AD efficiency and net energy balance.
Smith S, Rigby H, 2020, The significance of cadmium entering the human food chain via livestock ingestion from the agricultural use of biosolids, with special reference to the UK, Environment International, Vol: 143, Pages: 1-10, ISSN: 0160-4120
When biosolids are applied to agricultural soil, potentially toxic elements (PTEs) accumulate in the topsoil, although it takes many repeated applications to reach soil limit values. Two programmes of UK government-funded research were commissioned in the 1990s to investigate the transfer of PTEs to the food chain via ingestion by sheep grazing biosolids- amended soil. Here, we critically re-examine this evidence in the light of other published work and current food quality standards. This was particularly motivated by the need to determine the safety of biosolids controls on PTEs in relation to revised and stricter European food quality controls for PTEs in foodstuff. The major pathway for transfer of PTEs to grazing livestock is via direct ingestion of biosolids or biosolids-amended soil from the soil surface. The main elements of concern for the human diet are cadmium (Cd) and lead (Pb), with Cd being the focus of the current paper. Animal ingestion of plant tissue is also a potential pathway for Cd exposure, which, unlike Pb, can transfer to crop tissues. The concentrations of Cd in the muscle tissue of sheep grazing biosolids-amended soil were generally small and similar to control values. Cadmium concentrations in sheep offal were below the maximum permitted concentration for human consumption. This was despite ingestion of soils exceeding the maximum permissible concentration for Cd in soil (3 mg kg-1 dry soil) by up to three times, at an ingestion rate of 10% total dietary dry matter intake. Grazing trials under practical conditions on high Cd soils demonstrated that the Cd concentrations in sheep offal remained below the food limit value for this element in offal from the combined intakes from biosolids-amended soil and herbage. Futhermore, given the substantial fall in environmental emissions and concentrations in biosolids of this element and, consequently, it cannot accumulate in soil to the limit value, biosolids Cd does not represent
Barber EA, Liu Z, Smith SR, 2020, Organic contaminant biodegradation by oxidoreductase enzymes in wastewater treatment, Microorganisms, Vol: 8, ISSN: 2076-2607
Organic contaminants (OCs), such as pharmaceuticals, personal care products, flame retardants, and plasticisers, are societally ubiquitous, environmentally hazardous, and structurally diverse chemical compounds whose recalcitrance to conventional wastewater treatment necessitates the development of more effective remedial alternatives. The engineered application of ligninolytic oxidoreductase fungal enzymes, principally white-rot laccase, lignin peroxidase, and manganese peroxidase, has been identified as a particularly promising approach for OC remediation due to their strong oxidative power, broad substrate specificity, low energy consumption, environmental benignity, and cultivability from lignocellulosic waste. By applying an understanding of the mechanisms by which substrate properties influence enzyme activity, a set of semi-quantitative physicochemical criteria (redox potential, hydrophobicity, steric bulk and pKa) was formulated, against which the oxidoreductase degradation susceptibility of twenty-five representative OCs was assessed. Ionisable, compact, and electron donating group (EDG) rich pharmaceuticals and antibiotics were judged the most susceptible, whilst hydrophilic, bulky, and electron withdrawing group (EWG) rich polyhalogenated compounds were judged the least susceptible. OC susceptibility scores were in general agreement with the removal rates reported for experimental oxidoreductase treatments (R2 = 0.60). Based on this fundamental knowledge, and recent developments in enzyme immobilisation techniques, microbiological enzymic treatment strategies are proposed to formulate a new generation of biological wastewater treatment processes for the biodegradation of environmentally challenging OC compounds.
Liu Z, Smith SR, 2020, Enzyme activity of waste activated sludge extracts., Water Sci Technol, Vol: 80, Pages: 1861-1869, ISSN: 0273-1223
Wastewater treatment and generated biological sludge provide an alternative source of enzymes to conventional industrial production methods. Here, we present a protocol for extracting enzymes from activated sludge using ultrasonication and surfactant treatment. Under optimum conditions, ultrasound disruption of activated sludge gave recovery rates of protease and cellulase enzymes equivalent to 63.1% and ∼100%, respectively. The extracting of enzymes from activated sludge represents a potentially significant, high-value, resource recovery option for biological sludge generated by municipal wastewater treatment.
Reyna-Bensusan N, Wilson DC, Davy PM, et al., 2019, Experimental measurements of black carbon emission factors to estimate the global impact of uncontrolled burning of waste, ATMOSPHERIC ENVIRONMENT, Vol: 213, Pages: 629-639, ISSN: 1352-2310
Open burning is a widely practiced method of solid waste disposal in many regions of the world and represents a significant source of air pollution. Black carbon (BC) is a particularly serious air pollutant emitted from the uncontrolled burning of waste in open fires because it has a global warming potential (GWP) up to 5000 times greater than carbon dioxide (CO2) and is also linked to detrimental health impacts. However, few quantitative measurements of BC from open burning have been completed to establish the extent and impacts of this emission source on the environment. Emission factors (EFs) for BC from burning mixed solid waste samples were measured in the laboratory based on waste compositions in a representative developing country (Mexico). Black carbon EFs were also derived for individual waste types, including: green waste, different types of plastics, textiles and paper and cardboard. Individual waste BC EFs were combined using waste composition data from different areas of the world to estimate regional and global BC emissions from this source. The results demonstrated that BC emissions from open burning of waste have a significant climate impact, equivalent to 2–10% of global CO2Eq emissions. Global BC CO2Eq emissions from burning waste are 2–8 times larger compared to methane (CH4) CO2Eq emissions arising from the decomposition of equivalent amounts of combustible biodegradable waste disposed at dumpsites. Action to reduce open burning of waste would have a significant and immediate benefit to improving air quality and reducing the potential impact on climate change.
Grimes SM, Ciuffa F, Cooper J, et al., 2018, Development of a vacuum-packing system for food waste from urban catering facilities, Proceedings of the Institution of Civil Engineers. Waste and Resource Management., Vol: 171, Pages: 114-120, ISSN: 1747-6526
A novel vacuum-packing system is developed for food waste storage and collection under the conditions found in high-density urban and metropolitan catering establishments that has the following beneficial outcomes: (a) a reduction of 38% in the volume of food waste to be stored for collection; (b) a reduction in the physical space required on-site for storage of multiple vacuum packs of waste; (c) containment of the food waste stored in sanitised conditions, thus maintaining the integrity of the waste and extending the useful life of the waste in terms of its ideal composition for optimum beneficial recovery by anaerobic digestion or in-vessel composting, and reducing problems due to odour and vermin; and (d) reduction in the number of vehicle movements required to transfer the wastes to treatment facilities and their environmental impacts, while also achieving savings of £13–16 per bin lift in London, along with a considerable reduction in overall cost.
Kong FE, Deighton MA, Thurbon NA, et al., 2018, Cryptosporidium parvum decay during air drying and stockpiling of mesophilic anaerobically digested sewage sludge in a simulation experiment and oocyst counts in sludge collected from operational treatment lagoons in Victoria, Australia., Journal of Water and Health, Vol: 16, Pages: 435-448, ISSN: 1477-8920
The inactivation of Cryptosporidium species oocysts during sewage sludge treatment is important to protect human health when the residual biosolids are applied to agricultural land. Quantifying the decay of Cryptosporidium species during sludge treatment for microbiological assurance purposes is difficult if low numbers are present in wastewater. The rate of decay of Cryptosporidium parvum oocysts during solar/air drying treatment and in sludge stockpiles in temperate environment conditions was simulated in laboratory inoculation experiments using sludge sampled from a mesophilic anaerobic digester. Oocyst numbers were also determined in settled lagoon sludge samples collected from three operational rural wastewater treatment plants (WWTPs). C. parvum oocysts were enumerated by immunomagnetic separation followed by staining with vital dyes and examination by confocal laser scanning microscopy. An air-drying/storage period equivalent to 11 weeks was required for a 1 log10 reduction of viable oocysts inoculated into digested sludge. Oocyst viability in air-dried and stored digested sludge decreased with time, but was independent of sludge desiccation and dry solids (DS) content. No oocysts were detected in sludge samples collected from the anaerobic digester, and the average concentration of oocysts found in settled lagoon sludge from the rural WWTP was 4.6 × 102 oocysts/g DS.
Reyna-Bensusan N, Wilson DC, Smith SR, 2018, Uncontrolled burning of solid waste by households in Mexico is a significant contributor to climate change in the country., Environmental Research, Vol: 163, Pages: 280-288, ISSN: 0013-9351
Uncontrolled burning of municipal solid waste (MSW) is an important source of air pollution and is wide spread in many developing countries, but only limited data quantify the extent of domestic open burning of household waste. Here, we present some of the first field data to be reported on the uncontrolled domestic burning of waste. A representative community of Mexico (Huejutla de Reyes Municipality) was investigated and household surveys, interviews with waste operators and a waste characterisation analysis were completed to assess the extent of, and factors controlling, the open burning of waste. Waste collection provision to rural communities was very limited and, consequently 92% of households in rural areas reported that they disposed of waste by uncontrolled burning in backyards or unofficial dumps. Overall, 24% of the total MSW generated in the Municipality was disposed by uncontrolled burning. Urban and periurban areas received twice-weekly collections and the rate of uncontrolled burning was considerably smaller compared to rural households, corresponding to approximately 2% of total waste generation. Carbon equivalency calculations showed that burning waste in backyards represented approximately 6% of the total and 8.5% of fuel related CO2Eq emissions by the municipality. Moreover, the equivalent carbon dioxide (CO2Eq) from black carbon (BC) emitted by uncontrolled burning in backyards was over fifteen times larger compared to methane (CH4) potentially released from equivalent amounts of combustible biodegradable waste disposal at the official dumpsite. An assessment of local respiratory health data showed the incidence of disease was higher in rural than in urban areas, when the opposite trend is typically observed in the international literature; given the high rate of burning activity found in rural areas we suggest that open burning of waste could be a major reason for the apparent poorer respiratory health status of the rural population and requires
Wilson DC, Kanjogera JB, Soos R, et al., 2017, Operator models for delivering municipal solid waste management services in developing countries. Part A: The evidence base, Waste Management and Research, Vol: 35, Pages: 820-841, ISSN: 0734-242X
This article presents the evidence base for ‘operator models’ – that is, how to deliver a sustainable service through the interaction of the ‘client’, ‘revenue collector’ and ‘operator’ functions – for municipal solid waste management in emerging and developing countries. The companion article addresses a selection of locally appropriate operator models. The evidence shows that no ‘standard’ operator model is effective in all developing countries and circumstances. Each city uses a mix of different operator models; 134 cases showed on average 2.5 models per city, each applying to different elements of municipal solid waste management – that is, street sweeping, primary collection, secondary collection, transfer, recycling, resource recovery and disposal or a combination. Operator models were analysed in detail for 28 case studies; the article summarises evidence across all elements and in more detail for waste collection. Operators fall into three main groups: The public sector, formal private sector, and micro-service providers including micro-, community-based and informal enterprises. Micro-service providers emerge as a common group; they are effective in expanding primary collection service coverage into poor- or peri-urban neighbourhoods and in delivering recycling. Both public and private sector operators can deliver effective services in the appropriate situation; what matters more is a strong client organisation responsible for municipal solid waste management within the municipality, with stable political and financial backing and capacity to manage service delivery. Revenue collection is also integral to operator models: Generally the municipality pays the operator from direct charges and/or indirect taxes, rather than the operator collecting fees directly from the service user.
Liu J, Gao Y, Pearce P, et al., 2017, Statistical modelling anaerobic digestion for process optimization and bench-marking: a case study of E. coli inactivation across all Thames Water conventional sewage sludge treatment sites, Water and Environment Journal, Vol: 31, Pages: 498-507, ISSN: 1747-6593
Untreated sewage sludge potentially contains a wide range of enteric pathogens that present a risk to human health. Mesophilic anaerobic digestion (MAD) is the most-favoured process for sewage sludge treatment in the United Kingdom. It is a well-established approach to sludge stabilisation, but the mechanisms responsible for pathogen removal are poorly understood. Operational data collected by Thames Water from conventional MAD sites were statistically scrutinised to examine the effects of primary and secondary digestion on the removal of the enteric indicator bacteria, Escherichia coli, by using the IBM SPSS statistical software package for ANOVA, post-hoc and multiple regression analysis. The results showed that the process temperature conditions at the MAD plants were equivalent to or exceeded the minimum estimated by the analysis necessary to comply with the 2 log10 removal standard for E. coli. The results also showed that primary digestion conditions (specifically temperature) sublethally damaged E. coli and increased decay in secondary digestion and therefore over the whole digestion process.
Unc A, Alonso Camargo-Valero M, Smith SR, 2017, Algal Research, Special Issue Editorial: Wastewater and Algae; Risk, biofuels and long-term sustainability, Algal Research-Biomass Biofuels and Bioproducts, Vol: 24, Pages: A1-A1, ISSN: 2211-9264
Unc A, Monfet E, Potter A, et al., 2017, Note to Editor: Microalgae cultivation for wastewater treatment and biofuel production: a bibliographic overview of past and current trends, Algal Research-Biomass Biofuels and Bioproducts, Vol: 24, Pages: A2-A7, ISSN: 2211-9264
Irwin R, Surapaneni A, Smith D, et al., 2017, Verification of an alternative sludge treatment process for pathogen reduction at two wastewater treatment plants in Victoria, Australia, Journal of Water and Health, Vol: 15, Pages: 626-637, ISSN: 1477-8920
At South East Water wastewater treatment plants (WwTPs) in Victoria, Australia, biosolids are stockpiled for three years in compliance with the State guidelines to achieve the highest pathogen reduction grade (T1), suitable for unrestricted use in agriculture and landscaping. However, extended stockpiling is costly, may increase odour nuisance and greenhouse gas emissions, and reduces the fertiliser value of the biosolids. A verification programme of sampling and analysis for enteric pathogens was conducted at two WwTPs where sludge is treated by aerobic and anaerobic digestion, air drying (in drying pans or solar drying sheds) and stockpiling, to enumerate and, if present, monitor the decay of a range of enteric pathogens and parasites. The sludge treatment processes at both WwTPs achieved T1 grade biosolids with respect to prescribed pathogenic bacterial numbers (<1 Salmonella spp. 50 g−1 dry solids (DS) and <100 Escherichia coli g−1 DS) and >3 log10 enteric virus reduction after a storage period of one year. No Ascaris eggs were detected in the influent to the WwTPs, confirming previous studies that the presence of helminth infections in Victoria is extremely low and that Ascaris is not applicable as a control criterion for the microbiological quality of biosolids in the region.
Kumar S, Smith SR, Fowler G, et al., 2017, Challenges and opportunities associated with waste management in India, Royal Society Open Science, Vol: 4, ISSN: 2054-5703
India faces major environmental challenges associated withwaste generation and inadequate waste collection, transport,treatment and disposal. Current systems in India cannotcope with the volumes of waste generated by an increasingurban population, and this impacts on the environment andpublic health. The challenges and barriers are significant,but so are the opportunities. This paper reports on aninternational seminar on ‘Sustainable solid waste managementfor cities: opportunities in South Asian Association for RegionalCooperation (SAARC) countries’ organized by the Councilof Scientific and Industrial Research-National EnvironmentalEngineering Research Institute and the Royal Society. A priorityis to move from reliance on waste dumps that offer noenvironmental protection, to waste management systems thatretain useful resources within the economy. Waste segregationat source and use of specialized waste processing facilitiesto separate recyclable materials has a key role. Disposal ofresidual waste after extraction of material resources needsengineered landfill sites and/or investment in waste-to-energyfacilities. The potential for energy generation from landfill viamethane extraction or thermal treatment is a major opportunity,but a key barrier is the shortage of qualified engineers andenvironmental professionals with the experience to deliverimproved waste management systems in India.
Rigby H, Clarke BO, Pritchard DL, et al., 2016, A critical review of nitrogen mineralization in biosolids-amended soil, the associated fertilizer value for crop production and potential for emissions to the environment, SCIENCE OF THE TOTAL ENVIRONMENT, Vol: 541, Pages: 1310-1338, ISSN: 0048-9697
Rigby H, Dowding A, Fernandes A, et al., 2015, Organic Contaminant Content and Physico-Chemical Characteristics of Waste Materials Recycled in Agriculture, Agriculture, Vol: 5, Pages: 1289-1328, ISSN: 2077-0472
A range of wastes representative of materials currently applied, or with future potential to be applied, to agricultural land in the UK as fertilisers and soil improvers or used as animal bedding in livestock production, were investigated. In addition to full physico-chemical characterization, the materials were analysed for a suite of priority organic contaminants. In general, contaminants were present at relatively low concentrations. For example, for biosolids and compost-like-output (CLO), concentrations of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs) were approximately 1−10 and 5–50 times lower, respectively, than various proposed or implemented European limit values for these contaminants in biosolids or composts applied to agricultural land. However, the technical basis for these limits may require re-evaluation in some cases. Polybrominated, and mixed halogenated, dibenzo-p-dioxins/dibenzofurans are not currently considered in risk assessments of dioxins and dioxin-like chemicals, but were detected at relatively high concentrations compared with PCDD/Fs in the biosolids and CLOs and their potential contribution to the overall toxic equivalency is assessed. Other ‘emerging’ contaminants, such as organophosphate flame retardants, were detected in several of the waste materials, and their potential significance is discussed. The study is part of a wider research programme that will provide evidence that is expected to improve confidence in the use of waste-derived materials in agriculture and to establish guidelines to protect the food chain where necessary.
Angelonidi E, Smith SR, 2015, A comparison of wet and dry anaerobic digestion processes for the treatment of municipal solid waste and food waste, WATER AND ENVIRONMENT JOURNAL, Vol: 29, Pages: 549-557, ISSN: 1747-6585
Rigby HL, Acker S, Dowding A, et al., 2015, The physico-chemical properties and concentrations of organic contaminants in waste materials recycled in agriculture, Tinos2015 3rd International Conference on Sustainable Solid Waste Management
Brito LM, Mourao I, Coutinho J, et al., 2015, Co-composting of invasive Acacia longifolia with pine bark for horticultural use, ENVIRONMENTAL TECHNOLOGY, Vol: 36, Pages: 1632-1642, ISSN: 0959-3330
Rigby HL, Acker S, Dowding A, et al., 2015, Investigation of the Potential Transfer and Uptake of Contaminants into Food Arising from the use of Biosolids and other Recycled Wastes in Agriculture, SludgeTech
Orthodoxou D, Pettitt TR, Fuller M, et al., 2015, An Investigation of Some Critical Physico-chemical Parameters Influencing the Operational Rotary In-vessel Composting of Food Waste by a Small-to-Medium Sized Enterprise, WASTE AND BIOMASS VALORIZATION, Vol: 6, Pages: 293-302, ISSN: 1877-2641
Karkashan A, Khallaf B, Morris J, et al., 2015, Comparison of methodologies for enumerating and detecting the viability of Ascaris eggs in sewage sludge by standard incubation-microscopy, the BacLight Live/Dead viability assay and other vital dyes, WATER RESEARCH, Vol: 68, Pages: 533-544, ISSN: 0043-1354
Mondal T, Rouch DA, Thurbon N, et al., 2015, Factors affecting decay of Salmonella Birkenhead and coliphage MS2 during mesophilic anaerobic digestion and air drying of sewage sludge, JOURNAL OF WATER AND HEALTH, Vol: 13, Pages: 459-472, ISSN: 1477-8920
Rigby H, Smith SR, 2014, The nitrogen fertiliser value and other agronomic benefits of industrial biowastes, NUTRIENT CYCLING IN AGROECOSYSTEMS, Vol: 98, Pages: 137-154, ISSN: 1385-1314
Rigby H, Smith SR, 2013, Nitrogen availability and indirect measurements of greenhouse gas emissions from aerobic and anaerobic biowaste digestates applied to agricultural soils, WASTE MANAGEMENT, Vol: 33, Pages: 2641-2652, ISSN: 0956-053X
Brito LM, Mourao I, Coutinho J, et al., 2013, Composting for management and resource recovery of invasive Acacia species, WASTE MANAGEMENT & RESEARCH, Vol: 31, Pages: 1125-1132, ISSN: 0734-242X
Sim NM, Wilson DC, Velis CA, et al., 2013, Waste management and recycling in the former Soviet Union: The City of Bishkek, Kyrgyz Republic (Kyrgyzstan), WASTE MANAGEMENT & RESEARCH, Vol: 31, Pages: 106-125, ISSN: 0734-242X
Abd El Lateef EM, Hall JE, Smith SR, et al., 2013, A survey of heavy metals content of soil and plants as affected by long-term application of sewage water. A case study
© Owned by the authors, published by EDP Sciences, 2014. As part of a four year study evaluating the practicability and value of sewage sludge use in Egypt, soil and plant surveys were carried out on a citrus plantation, irrigated with Cairo sewage since the 1920s, in order to evaluate the long-term accumulation of trace elements and heavy metals and their bioavailability. While total and DTPA soil concentrations correlated well, no relationship could be found between soil and plant tissue concentrations, despite elevated levels of heavy metals in the soil. Study of long-term contamination of soil with potentially toxic elements (PTEs) has not demonstrated a potential risk to crop quality and yield or human health from the slow accumulation of PTEs in sludge-treated agricultural soil. PTE concentrations in plant tissues remained low and within normal ranges despite significant increases in soil content after long-term irrigation with sewage effluent. Concentrations of PTEs in plant tissues were not related to total or DTPA extractable metals in contaminated soil. DTPA may not be a sufficiently reliable indicator of actual phytoavailability of trace elements in sludge-treated soil, although it is accepted that DTPA is widely used in nutrient diagnosis assessment. These data provide assurance about the minimal risk to the environment from trace elements and PTEs in sludge-treated agricultural soil, but a more detailed dietary analysis of Cd intakes under Egyptian conditions is recommended, following the approaches adopted in the UK and US for setting Cd soil limits or loading rates for this element.
Nicholson FA, Humphries S, Anthony SG, et al., 2012, A software tool for estimating the capacity of agricultural land in England and Wales for recycling organic materials (ALOWANCE), SOIL USE AND MANAGEMENT, Vol: 28, Pages: 307-317, ISSN: 0266-0032
Velis CA, Wilson DC, Rocca O, et al., 2012, An analytical framework and tool ('InteRa') for integrating the informal recycling sector in waste and resource management systems in developing countries, WASTE MANAGEMENT & RESEARCH, Vol: 30, Pages: 43-66, ISSN: 0734-242X
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