Residual Biosolids Research Articles

Impact of pH and removed filtrate on E. coli regrowth and microbial community during storage of electro-dewatered biosolids

Residual biosolids can be land applied if they meet microbiological requirements at the time of application. Electro-dewatering technology is shown to reduce biosolids bacterial counts to detection limits with little potential for bacterial regrowth during incubations. Here, we investigated the impacts on Escherichia coli regrowth and microbial communities of biosolids pH, removed nutrients via the filtrate, and inhibitory compounds produced in electro-dewatered biosolids. Findings suggest pH as the primary mechanism impacting E. coli regrowth in electro-dewatered biosolids. Propidium monoazide treatments were effective at removing DNA from dead cells, based on the removal of obligate anaerobes observed after anaerobic incubation. Analyses of high throughput sequenced data showed lower alpha-diversities associated with electro-dewatering treatment and incubation time. Moreover, biosolids pH and incubation period were the main factors contributing to the variations in microbial community compositions after incubation. Results highlight the role of electro-dewatered biosolids' low pH on inhibiting the regrowth of culturable bacteria as well as reducing the microbial community variance.

Effect of alkaline treatment on the removal of contaminants of emerging concern from municipal biosolids: Modelling and optimization of process parameters using RSM and ANN coupled GA

The current study aimed in enhancing the efficiency of alkaline treatment for CECs remediation in biosolids through the application of RSM and ANN. Due to the seasonal variation of CECs in biosolids, a complete CECs profile over a period of three years were performed. Out of 64 targeted CECs, 13 PhACs (70.1 μg/kg) and 10 pesticides (57.2 μg/kg) were detected in biosolids. In order to enhance the remediation efficiency of CECs by alkaline treatment, process parameters - pH (9.0–13.0), time (3.0–12.0 h) and biosolids age (1–28 days) were optimized by statistical modelling. Using Box-Behnken design, experiments were designed and the resultant data was employed as input for model building using RSM and ANN. The developed mathematical model for alkaline treatment of biosolids using ANN predicted CECs removal with 3.2-fold lower MSE and exhibited high regression coefficient (R2 > 0.99) than the conventional RSM model. Further, the multiparameter model was optimized for achieving maximum of 95.7 % CECs removal using ANN-GA. On analyzing the acute toxicity of alkaline treated residual biosolids under the optimized conditions, a reduction in LC50 by an average of 2.1-fold than initial biosolids was observed. This study not only established the application of statistical modelling in the development of an efficient remediation strategy for biosolids, which can be further applied for large-scale remediation process, but also proved the reliability and efficiency of ANN-GA.

Multi-Criteria Analysis and Consequential Lifecycle Assessment of Solid Waste Management

Based on a case study comparing different approaches for management of organic waste generated in the city of Rio de Janeiro, Brazil, this study proposes the combination of consequential lifecycle assessment (CLCA) and multicriteria decision analysis (MCDA). Compared approaches were landfilling with energy recovery from landfill gas, source segregation of organics for anaerobic digestion and use of digestate as fertilizer, and finally, post-sorting of organics and landfilling of residual bio-solids. Seven different impact categories were assessed in the CLCA. In addition, recovery of electricity and macro nutrients were included as additional impact categories. The use of VIP analysis facilitates the interpretation of results aggregating them under different conditions. Furthermore, approaches for ranking of considered impact categories could be carried out both for a local or a global perspective. This, and the possibility of easily including additional context derived evaluation parameters, clearly highlights the combination of CLCA and VIP analysis for decision support.

Effect of Substrate to Inoculum Ratio on Bioenergy Recovery from Food Waste, Yard Waste, and Biosolids by High Solids Anaerobic Digestion

Residual biosolids from wastewater treatment facilities and the organic fraction of municipal solid waste (OFMSW), such as food and yard wastes (FW and YW), are difficult to manage due to increased...

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

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.

Heavy metals and metalloids: Sources, risks and strategies to reduce their accumulation in horticultural crops

Abstract Food production in areas contaminated with heavy metals is associated with health risks because of their adverse effects on food safety and marketability, and on crop growth and yield quality. The present review focuses on sources and risks of heavy metals, mainly in cultivated fields in various regions, and strategies to reduce their accumulation in horticultural crops. The following heavy metals are discussed: arsenic (As), boron (B), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), mercury (Hg), molybdenum (Mo), nickel (Ni), strontium (Sr), tin (Sn), titanium (Ti), vanadium (V) and zinc (Zn). Heavy metal sources in the environment can originate from natural and anthropogenic activities. Their main natural enrichment in soils stems from parent-material weathering. However, in coastal areas, precipitation of sea spray may enrich soil with B. In contrast, the main anthropogenic sources of heavy metals in cultivated areas are irrigation with treated sewage water, application of residual biosolids, and atmospheric pollution. Plants absorb heavy metals predominantly through roots and, to a lesser extent, through leaves. Leaf uptake can occur through the stomata, cuticular cracks, ectodesmata, and aqueous pores. Heavy metal uptake may lead to their accumulation in vegetables and fruit trees, and their consequent introduction into the food chain, which is recognized as one of the major pathways for human exposure to them. This exposure can result in retardation, several types of cancer, kidney damage, endocrine disruption, and immunological and neurological effects. High concentrations of heavy metals can also affect the growth and yield of many crops: Zn and Cd decrease plant metabolic activity and induce oxidative damage; Cu generates oxidative stress and reactive oxygen species; Hg can induce visible injury and physiological disorders; Cr affects photosynthesis in terms of CO2 fixation, electron transport, photophosphorylation and enzyme activities; Pb induces plant abnormal morphology; Ni spoils the nutrient balance, resulting in disorders of cell membrane functions; Fe causes free radical production that irreversibly impairs cell structure and damages membranes, DNA and proteins; As causes leaf necrosis and wilting, followed by root discoloration and retardation of shoot growth. Therefore, international organizations, such as the US EPA and EU bodies, are working on regulating the maximum allowable levels of food pollutants. A number of direct (mycorrhiza, transgenic plants and grafting) approaches can be deployed to overcome problems of heavy metal contamination in horticulture.

Biosolids-Derived Biochar for Triclosan Removal from Wastewater

Abstract Micropollutants, including antibiotics, hormones, pharmaceuticals, and personal care products, are discharged into the environment with liquid and solid effluent streams from water resource recovery facilities (WRRFs). The objective of this research was to determine whether biosolids-derived biochar (BS-biochar) could be used as a sorbent in continuous flow-through columns to remove micropollutants as a polishing step for wastewater treatment. Triclosan (TCS) was selected as a representative micropollutant due to frequent detection in liquid effluents, residual biosolids, and surface waters. Bench-scale column experiments were conducted to determine the effect of flow rate and competition due to the presence of other organic micropollutants and inorganic nutrients on TCS adsorption to BS-biochar. TCS removal efficiency was compared in Milli-Q water and secondary wastewater effluent by using two commercial adsorbents: a granular activated carbon and a wood-based biochar. Increased removal of TCS w...

Energy use and carbon footprints differ dramatically for diverse wastewater-derived carbonaceous substrates: An integrated exploration of biokinetics and life-cycle assessment

Energy neutrality and reduction of carbon emissions are significant challenges to the enhanced sustainability of wastewater treatment plants (WWTPs). Harvesting energy from wastewater carbonaceous substrates can offset energy demands and enable net power generation; yet, there is limited research about how carbonaceous substrates influence energy and carbon implications of WWTPs with integrated energy recovery at systems-level. Consequently, this research uses biokinetics modelling and life cycle assessment philology to explore this notion, by tracing and assessing the quantitative flows of energy embodied or captured, and by exploring the carbon footprint throughout an energy-intensive activated sludge process with integrated energy recovery facilities. The results indicate that energy use and carbon footprint per cubic meter of wastewater treated, varies markedly with the carbon substrate. Compared with systems driven with proteins, carbohydrates or other short-chain fatty acids, systems fed with acetic acid realized energy neutrality with maximal net gain of power from methane combustion (0.198 kWh) and incineration of residual biosolids (0.153 kWh); and also achieved a negative carbon footprint (72.6 g CO2). The findings from this work help us to better understand and develop new technical schemes for improving the energy efficiency of WWTPs by repurposing the stream of carbon substrates across systems.

Fate of trace organic contaminants in oxic-settling-anoxic (OSA) process applied for biosolids reduction during wastewater treatment

This study investigated the fate of trace organic contaminants (TrOCs) in an oxic-settling-anoxic (OSA) process consisting of a sequencing batch reactor (SBR) with external aerobic/anoxic and anoxic reactors. OSA did not negatively affect TrOC removal of the SBR. Generally, low TrOC removal was observed under anoxic and low substrate conditions, implicating the role of co-metabolism in TrOC biodegradation. Several TrOCs that were recalcitrant in the SBR (e.g., benzotriazole) were biodegraded in the external aerobic/anoxic reactor. Some hydrophobic TrOCs (e.g., triclosan) were desorbed in the anoxic reactor possibly due to loss of sorption sites through volatile solids destruction. In OSA, the sludge was discharged from the aerobic/anoxic reactor which contained lower concentration of TrOCs (e.g., triclosan and triclocarban) than that of the control aerobic digester, suggesting that OSA can also help to reduce TrOC concentration in residual biosolids.

Emerging investigators series: pyrolysis removes common microconstituents triclocarban, triclosan, and nonylphenol from biosolids

Pyrolysis could be used as a biosolids processing step that reduces the amount of organic microconstituents discharged to the environment with residual biosolids.

Impact of Joule Heating and pH on Biosolids Electro-Dewatering.

Electro-dewatering (ED) is a novel technology to reduce the overall costs of residual biosolids processing, transport, and disposal. In this study, we investigated Joule heating and pH as parameters controlling the dewaterability limit, dewatering rate, and energy efficiency. Temperature-controlled electrodes revealed that Joule heating enhances water removal by increasing evaporation and electro-osmotic flow. High temperatures increased the dewatering rate, but had little impact on the dewaterability limit and energy efficiency. Analysis of horizontal layers after 15-min ED suggests electro-osmotic flow reversal, as evidenced by a shifting of the point of minimum moisture content from the anode toward the cathode. This flow reversal was also confirmed by the pH at the anode being below the isoelectric point, as ascertained by pH titration. The important role of pH on ED was further studied by adding acid/base solutions to biosolids prior to ED. An acidic pH reduced the biosolids charge while simultaneously increasing the dewatering efficiency. Thus, process optimization depends on trade-offs between speed and efficiency, according to physicochemical properties of the biosolids microstructure.

A unified method to process biosolids samples for the recovery of bacterial, viral, and helminths pathogens

For land application, biosolids are classified as Class A or Class B based on the levels of bacterial, viral, and helminths pathogens in residual biosolids. The current EPA methods for the detection of these groups of pathogens in biosolids include discrete steps. Therefore, a separate sample is processed independently to quantify the number of each group of the pathogens in biosolids. The aim of the study was to develop a unified method for simultaneous processing of a single biosolids sample to recover bacterial, viral, and helminths pathogens. At the first stage for developing a simultaneous method, nine eluents were compared for their efficiency to recover viruses from a 100 gm spiked biosolids sample. In the second stage, the three top performing eluents were thoroughly evaluated for the recovery of bacteria, viruses, and helminthes. For all three groups of pathogens, the glycine-based eluent provided higher recovery than the beef extract-based eluent. Additional experiments were performed to optimize performance of glycine-based eluent under various procedural factors such as, solids to eluent ratio, stir time, and centrifugation conditions. Last, the new method was directly compared with the EPA methods for the recovery of the three groups of pathogens spiked in duplicate samples of biosolids collected from different sources. For viruses, the new method yielded up to 10% higher recoveries than the EPA method. For bacteria and helminths, recoveries were 74% and 83% by the new method compared to 34% and 68% by the EPA method, respectively. The unified sample processing method significantly reduces the time required for processing biosolids samples for different groups of pathogens; it is less impacted by the intrinsic variability of samples, while providing higher yields (P = 0.05) and greater consistency than the current EPA methods.

Using a Pulsed Electric Field as a Pretreatment for Improved Biosolids Digestion and Methanogenesis

Researchers tested using pulsed electric field (PEF) technology to enhance conversion of organic solids material in waste activated sludge (WAS) and pig manure to soluble and colloidal forms, which are more bioavailable for methane production during subsequent anaerobic digestion. Operating parameters were varied from 1.1 to 19.8 kWhr/m3 to show the influence amount of treatment has on soluble chemical oxygen demand (SCOD), small colloidal solids, and methane production via the biochemical methane potential test. When PEF treatment exceeded a threshold, which was approximately 10 kWhr/m3, focused pulsed treatment solubilized approximately 10% of the total COD, increasing SCOD from as low as 20 mg/L to more than 1000 mg/L. The process also disrupted a larger portion of the volatile suspended solids (VSS) to form small colloids not measured by the VSS assay (between 0.2 and 1.2 microm). The effects increased the biological methane potential of the samples significantly: by 80% for pig manure and 100% for WAS after 25 to 30 days. These results support the conclusion that PEF pretreatment before anaerobic digestion has the potential to significantly improve digester performance, resulting in added methane production and decreased residual biosolids.

Fate of applied biosolids nitrogen in a cut and remove forage system on an alluvial clay loam soil

The fate of nitrogen (N) applied in biosolids was investigated in a forage production system on an alluvial clay loam soil in south-eastern Queensland, Australia. Biosolids were applied in October 2002 at rates of 6, 12, 36, and 54 dry t/ha for aerobically digested biosolids (AE) and 8, 16, 48, and 72 dry t/ha for anaerobically digested biosolids (AN). Rates were based on multiples of the Nitrogen Limited Biosolids Application rate (0.5, 1, 3, and 4.5NLBAR) for each type of biosolid. The experiment included an unfertilised control and a fertilised control that received multiple applications of synthetic fertiliser. Forage sorghum was planted 1 week after biosolids application and harvested 4 times between December 2002 and May 2003. Dry matter production was significantly greater from the biosolids-treated plots (21–27 t/ha) than from the unfertilised (16 t/ha) and fertilised (18 t/ha) controls. The harvested plant material removed an extra 148–488 kg N from the biosolids-treated plots. Partial N budgets were calculated for the 1NLBAR and 4.5NLBAR treatments for each biosolids type at the end of the crop season. Crop removal only accounted for 25–33% of the applied N in the 1NLBAR treatments and as low as 8–15% with 4.5NLBAR. Residual biosolids N was predominantly in the form of organic N (38–51% of applied biosolids N), although there was also a significant proportion (10–23%) as NO3-N, predominantly in the top 0.90 m of the soil profile. From 12 to 29% of applied N was unaccounted for, and presumed to be lost as gaseous nitrogen and/or ammonia, as a consequence of volatilisation or denitrification, respectively. In-season mineralisation of organic N in biosolids was 43–59% of the applied organic N, which was much greater than the 15% (AN)–25% (AE) expected, based on current NLBAR calculation methods. Excessive biosolids application produced little additional biomass but led to high soil mineral N concentrations that were vulnerable to multiple loss pathways. Queensland Guidelines need to account for higher rates of mineralisation and losses via denitrification and volatilisation and should therefore encourage lower application rates to achieve optimal plant growth and minimise the potential for detrimental impacts on the environment.

Using a Pulsed Electric Field as a Pretreatment for Improved Biosolids Digestion and Methanogenesis

Researchers tested using pulsed electric field (PEF) technology to enhance conversion of organic solids material in waste activated sludge (WAS) and pig manure to soluble and colloidal forms, which are more bioavailable for methane production during subsequent anaerobic digestion. Operating parameters were varied from 1.1 to 19.8 kWhr/m 3 to show the influence amount of treatment has on soluble chemical oxygen demand (SCOD), small colloidal solids, and methane production via the biochemical methane potential test. When PEF treatment exceeded a threshold, which was approximately 10 kWhr/m 3 , focused pulsed treatment solubilized approximately 10% of the total COD, increasing SCOD from as low as 20 mg/L to more than 1000 mg/L. The process also disrupted a larger portion of the volatile suspended solids (VSS) to form small colloids not measured by the VSS assay (between 0.2 and 1.2 μm). The effects increased the biological methane potential of the samples significantly: by 80% for pig manure and 100% for WAS after 25 to 30 days. These results support the conclusion that PEF pretreatment before anaerobic digestion has the potential to significantly improve digester performance, resulting in added methane production and decreased residual biosolids.

97/03876 Combustion of residual biosolids from a high solids anaerobic digestion/aerobic composting process

Prospects are examined for utilizing renewable energy crops as a source of liquid fuel to mitigate greenhouse gas emissions from mobile sources and reduce dependence on imported petroleum. Fuel-cell vehicles would provide a promising technology for coping with the environmental and economic effects of an expanding vehicle fleet and a decreasing petroleum supply. Fueled with methanol or hydrogen derived from biomass, fuel cells can also effectively address the problem of CO2 emissions from that fleet. The extent to which this combination might affect petroleum displacement depends on the amount of biomass that could be produced and the efficiency of its conversion to a fuel compatible with fuel cells. Reduction of net CO2 emissions by the best current bio-fuel technology will be limited by biomass supply. Biomass conversion efficiency, petroleum displacement and overall net CO2 emission reduction can be improved, and the cost of fuel minimized, by use of natural gas as a co-feedstock. The extra hydrogen provided by natural gas allows these improvements by eliminating the partial shift of CO to CO2 that is otherwise necessary; elimination of that step and additional in situ leveraging of fuel yield by conventional reforming reactions also reduce the production cost. A thermochemical process utilizing both biomass and natural gas as co-feedstocks is compared with other options for methanol production and CO2 mitigation using either biomass or natural gas alone. Use of natural gas as co-feedstock makes possible the additional environmental advantage of utilizing waste methane from landfills and waste-water treatment facilities, as well as the carbonaceous solid wastes and sludge from those facilities, for conversion to clean transportation fuel. Greenhouse gas emissions from these important municipal sources can thus be concurrently reduced, together with landfill disposal requirements.

Combustion of residual biosolids from a high solids anaerobic digestion/aerobic composting process

A humus consisting of aerobically stabilized anaerobic digester effluent was burned in two laboratory test facilities to evaluate possible problems in using the humus as fuel in boilers. An atmospheric circulating fluidized-bed combustor (FBC) was used to assess possible bed agglomeration when using alumina-silicate bed media. A multi-fuel capable entrained flow combustor (MFC) with electrically heated walls simulating a boiler was used with air-cooled tubular probes to evaluate potential ash deposition on heat exchangers. Low heating value of the humus led to poor temperature control in the FBC when burned alone. Tests of the humus blended 50% by weight with wood were also carried out in the FBC. No evidence of bed agglomeration was found in the FBC with either humus alone or blended with wood at temperatures up to 900°C; the maximum tested. Bed-drain rate was nearly equal to fuel-ash feed rate to maintain constant bed pressure drop due to the high sand fraction in the humus. Deposits collected on the probes in the MFC experiment were enriched in alkali-sulfate, as were the fine fractions of fly-ash samples. Deposition rates were not established due to particle-induced abrasion of deposits from the heavy sand fraction of the fuel, but at least moderate alkali-sulfate deposition can be anticipated if humus is burned in commercial units.

Decomposition of Biosolids in a Disposal Site Soil

AbstractThe objectives of this study were to determine if residual biosolids in a disposal site soil altered fresh biosolid decomposition and characterize the decomposition behavior of the residual biosolids in that soil. This information is requisite to predicting the impact of residual biosolids on release of N via net N mineralization from fresh and residual biosolids at the disposal site. Aerobically digested municipal sewage sludge from Laredo, TX, was incubated in LaGloria silty clay loam soil (coarse‐silty, mixed, hyperthermic fluventic Ustochrepts) from three locations within the disposal area. Sites 1 and 2 had been amended with biosolids at disposal rates of 647 and 418 Mg ha−1, respectively, over a 7‐yr period while Site 3 was the control. Carbon dioxide evolution was monitored for 62 d and decomposition of fresh biosolid was evaluated using first‐order kinetics for simultaneous and sequential decomposition models. Decomposition of the “active” and “total” residual biomass pools was also assessed. Decomposition of the fresh biosolid was characterized as a two phase (rapid and slow fractions) process. The rate constants for these phases and percentages of biosolid in the rapid fraction were independent of previous additions for this biosolid/soil combination. The active pool or the residual biosolid that was most labile was from 6 to 10% of the total residual biosolid C pool. First‐order rate constants for the total pool of residual biosolids approached those that have been used for more labile portions of soil organic matter.

Pollution prevention: a winning strategy for the protection of the environment

This case study presents the development and implementation of the County Sanitation Districts of Orange County (Districts) Pollution Prevention Program (P3) aimed at reducing the environmental release of pollutants. The P3 has been integrated in the Districts' environmental management program and incorporates the goals of the Districts' 30-year Master Plan called 2020 Vision. The Districts take a multi-media approach to environmental protection giving equal importance to emissions to air, water or the land. The Districts' P3 efforts, applied in combination with an aggressive Source Control Program, has resulted in significant reductions in heavy metals and other pollutant discharges to the environment. The P3 is a major element of the Districts' Source Control Program. During the past seven years, pollution prevention (the management of waste generation or reduction of waste before it is generated) has proven to be the most effective strategy to protect the environment. The Program has resulted in reductions in influent loadings of heavy metals and other pollutants of concern, and an improving record of compliance by major industrial dischargers. The reduction in metals and other pollutants has resulted in quantifiable improvements in environmental conditions in the marine environment (in the vicinity of the discharge) several miles offshore near the ocean outfall, in reduced air emissions from the treatment plants, and in the concentrations of heavy metals in the residual biosolids produced for recycling. Long-term monitoring data shows improvements in effluent toxicity (as measured by fish survival), reductions in the concentrations of metals in sediments around the ocean outfall and long-term gradual improvements in biological conditions as measured by the number of species of benthic invertebrates. Data on the trends for each of these and other conditions, are presented along with the specific methods employed to achieve the reductions from industrial dischargers. The successes of P3 were acknowledged by the United States Environmental Protection Agency (EPA), which awarded the Districts the Administrator's national 1992 Pollution Prevention Achievement Award.