Biosolids Stabilization Research Articles

Investigating the synergic role of asynchronous dosed protease and lysozyme for facilitating excess sludge solubilization and acidogenic fermentation

Improving the anaerobic fermentation (AF) efficiency of excess sludge (ES) is essential for attaining biosolid minimization, stabilization, resource recovery, and carbon-emission reduction. Along these lines, here, the synergistic mechanism of protease and lysozyme for enhancing hydrolysis and AF efficiency with better recovery of volatile fatty acids (VFAs) was thoroughly investigated. Single lysozyme was capable of reducing the zeta potential and fractal dimension when dosed into the ES-AF system, which was beneficial for increasing the contact probability between proteases and extracellular proteins. Moreover, the weight-averaged molecular weight of the loosely-bound extracellular polymeric substance (LB-EPS) reduced from 1867 to 1490 in the protease-AF group, which facilitated the penetration of EPS by the lysozyme. The soluble DNA and extracellular DNA (eDNA) of the enzyme cocktail pretreated group increased by 23.24 % and 77.09 %, and the cell viability decreased after 6-hour hydrolysis, demonstrating a better hydrolysis efficiency. Remarkably, the asynchronous dosed enzyme cocktail pretreatment was proven a better strategy to enhance both the solubilization and hydrolysis processes since the synergistic effect of these two enzymes can exclude the mutual interference. As a result, the VFAs were increased by 1.26 times higher than the blank group. The underlying mechanism of an environmental-friendly and effective strategy was examined to promote ES hydrolysis and acidogenic fermentation, which was beneficial for the recovery of VFAs and carbon-emission reduction.

Pyrolysis-A tool in the wastewater solids handling portfolio, not a silver bullet: Benefits, drawbacks, and future directions.

Pyrolysis is the process whereby carbonaceous materials, such as biosolids, are heated between 400°C and 900°C in the absence of oxygen. Three main products are generated: a solid product called biochar, a py-liquid that consists of aqueous phase and non-aqueous phase liquid, and py-gas. The biochar holds value as a beneficial soil amendment and sequesters carbon. The py-liquid is potentially hazardous and needs to be dealt with (including potentially reducing it on-site via catalysis or thermal oxidation). Py-gas can be used on-site for energy recovery. Pyrolysis has gained recent interest due to concern over per- and polyfluoroalkyl substances (PFAS) in biosolids. Although pyrolysis can remove PFAS from biosolids, it has been shown to produce PFAS that reside in py-liquid, and the fate in py-gas remains a knowledge gap. More research is needed to help close the PFAS and fluorine mass balance through pyrolysis influent and effluent products because pyrolysis alone does not destroy all PFAS. The moisture content of biosolids substantially affects the energy balance for pyrolysis. Utilities that already produce a dried biosolids product are in a better position to install pyrolysis. Pyrolysis has both defined benefits (solids reduction, PFAS removal from biosolids, and biochar production) as well as remaining questions (the fate of PFAS in py-gas and py-liquid, mass balance on nutrients, and py-liquid handling options) that will be answered through more pilot and full-scale demonstrations. Regulations and local policies (such as carbon sequestration credits) could affect pyrolysis implementation. Pyrolysis should be considered as an option in the biosolids stabilization toolbox with application being based on individual circumstances of a utility (e.g., energy, moisture content of biosolids, PFAS). PRACTITIONER POINTS: Pyrolysis has known benefits but limited full-scale operational data. Pyrolysis removes PFAS from biochar, but PFAS fate in gas phase is unknown. Moisture content of influent feed solids affects energy balance of pyrolysis. Policy on PFAS, carbon sequestration, or renewable energy could impact pyrolysis.

Effect of biochar on the mitigation of organic volatile fatty acid emission during aerobic biostabilization of biosolids and the underlying mechanism

In order to declare the effect and the underlying mechanism of biochar amendment on volatile fatty acid (VFA) emission during aerobic biostabilization of biosolids, different types of biochar (i.e., wheat straw biochar [WHB], sawdust biochar [SDB], and food waste digestate biochar [FRB]; 5% in dry weight) on carbon transformation and VFA emissions during 45-day aerobic biostabilization of biosolids were investigated. The results showed that biochar amendment improved thermophilic phase evolution and product dephytotoxification. During the 45-day period, in comparison to control, biochar addition promoted CH4 reduction by 44.46%–76.90% and enhanced the content of total organic carbon reduction by 20.60%–56.80%. In addition, biochar addition lowered the emissions of acetic, propanoic, isobutyric, butyric, isovaleric, and valeric acids by respectively 23.43%–41.21%, 23.10%–43.92%, 42.62%–56.11%, 26.70%–58.20%, 10.56%–58.27%, and 33.74%–49.45% compared with control values. Moreover, biochar amendment facilitated organic matter humification during biosolid bioconversion as well. Among the applied types of biochar, SDB, with a higher surface area, was more efficient in organic matter degradation and VFA emission mitigation than WHB and FRB. In particular, biochar amendment increased the abundance and diversity of aerobic bacterial communities such as Acinetobacter, Desemzia, Georgenia, Nonomuraea, Psycharobacter, Planococcus, Paenisporosarcina, Physchrobacillus, Staphylococcus, Thermobifida, and Thermopolyspora, while inhibiting the reproduction of anaerobic bacteria including Bacillus, Bacteroides, Corynebacterium, Ruminofilibacter, and Terrisporobacter during biosolid stabilization, thus improving biosolid maturity and stabilization and reducing VFA emissions. These findings offer a novel method with appropriate recommendations for the use and the selection of biochar in increasing the efficiency of biosolid aerobic biostabilization.

Biosolids leachate variability, stabilization surrogates, and optical metric selection

Sludge and biosolids organic matter (OM) are increasingly assessed via optical measurements of associated leachates – especially at pilot and bench scales.

Dewatering, Stabilization, and Final Disposal of Waste Activated Sludge in Constructed Wetlands

Objective: This research aimed to assay the dehydration and stabilization of surplus biosolids from a wastewater activated sludge treatment plant, with sludge-treatment wetlands, at the Iguazú National Park (Misiones, Argentina). Materials and Methods: A 12-cell sludge-treatment reed beds (STRB) system was built and operated for four years. Afterwards, the accumulated sediments were analyzed for total solids (TS) concentration, volatile solids (VS) reduction, specific oxygen-uptake rate (SOUR), and heavy metals and pathogens concentrations. Results and Discussion: TS concentration increased from 0.55 % to 14.3 %, VS were reduced by 33.3 %, and SOUR lowered to 1.09 mg O2gTS-1 h-1. These figures and the final concentrations of heavy metals and pathogenic microorganisms (102 MPN E.coli.gTS-1) indicated a degree of stabilization and sanitation that allowed classifying these biosolids as Class A, according to the Argentine guidelines, National Resolution 410/18, and enabled their reuse for soil amendment in landscapes and other agronomic purposes. Conclusion: The technology tested showed good results applied under a tropical climate, with annual temperatures between 17 and 27 °C, rainfall of 1870 mm y-1, and planted with autochthonous vegetation. Furthermore, it allowed the reuse of 221 t (144 m3) of a harmless product in an environmentally sustainable way.

Identifying ranges of combined lime and heat treatments to achieve biosolids stabilization fecal coliform targets

To ensure safe reuse, biosolids are stabilized to reduce pathogens, odor, and volatile solids. Stabilization by lime addition have high material costs, high transportation costs, and loss of ammonia. Decreasing required lime additions would improve the sustainability of biosolids reuse. This study examined combining lime and heat treatment to reduce lime additions needed for required fecal coliform destruction. In contrast to the current best management practice requiring a pH of 12, fecal coliform reduction for final concentrations <1000 MPN/g (where MPN is most probable number) was achieved with pH as low as 10 when combined with a short (1-h) incubation at 60 °C. Analysis of D-values (the time required to destroy 1-log fecal coliform) supported a synergistic treatment response at moderate pH and heat treatments. Samples receiving higher temperature treatments had lower specific oxygen uptake rates, suggesting that readily-available carbon was lost during heat treatment. Samples with lower lime additions had higher final ammonia concentrations, which is a desired characteristic for biosolids reclaimed as a fertilizer. The study demonstrated that optimizing combined lime and heat stabilization can improve beneficial reuse as a means toward enhancing environmental sustainability and improving the circular economy.

Horizontal flow reactor optimization for biogas recovery during high solid organics fermentation: Rheological characteristic analyses

Continuous improvements in human living standards, water supply quality, and poor solid waste collection systems in China has led to increased production of municipal sewage sludge and organic solid waste (MOSW), which incurs a potential risk for human health and the environment. Solid anaerobic fermentation, which has exhibited advantageous energy recovery and biosolid stabilization, has been considered for urban organic solid waste treatment. The primary objective of this study was to optimize horizontal flow reactor operations for the efficient fermentation of high solid organics and subsequent biogas production via rheological characteristic analyses. The effects of operational parameters, such as paddle type, paddle diameter, pitch diameter ratio, stirring efficiency, torque, and power consumption, on the reactor performance were simulated using computational fluid dynamics (CFD). The solid content greatly influenced the rheological characteristics of the MOSW; increasing the solid content (5 %–30 %) of the MOSW led to a significant decline in the rheological index (0.532 to 0.224). The optimized parameters simulated by CFD included a screw-type stirring paddle with a pitch of 0.6 D, pitch of the screw with the value of 0.75 D, stirring shaft (set vertically and eccentrically downward) with the value of 0.15 D, and stirring speed less than 10 rpm. Moreover, the higher the consistency coefficient, the lower the rheological index and required power consumption. The reactor energy consumption analysis indicated that the average energy consumption can reach 48.20 kJ/m3 with an efficient operation.

Simultaneous quantification of five pharmaceuticals and personal care products in biosolids and their fate in thermo-alkaline treatment

The presence of pharmaceuticals and personal care products (PPCPs) in biosolids applied to farmland is of concern due to their potential accumulation in the environment and the subsequent effects on humans. Thermo-alkaline hydrolysis (TAH) is a method used for greater stabilization of biosolids after anaerobic digestion. In this work, the effect of TAH on five selected PPCPs including fluoroquinolone antibiotics, ciprofloxacin (CIP), and ofloxacin (OFLX), and three commonly used antimicrobial agents, miconazole (MIC), triclosan (TCS) and triclocarban (TCC) was evaluated. At the onset, extraction and analytical methods were optimized for maximum simultaneous recovery and LC-MS quantification of the target PPCPs from both water and biosolids for improved accuracy. The compounds were detected in the range of 54 ± 3 to 6166 ± 532 ng/g in raw biosoilds collected from a local WWTP. Next, batch control adsorption experiments of the selected PPCPs were conducted in various sludges, which indicated about 89%–98% sorption of the PPCPs onto solid phase due to their high octanol-water coefficients. Subsequently, thermo-alkaline (pH 9.5, 75 °C, 45 min) hydrolysis (TAH) was conducted to determine the extent of degradation of these compounds in deionized (DI) water and biosolids due to treatment. The degradation of these compounds due to TAH ranged from 42% to 99% and 37%–41% in pure water and biosolids, respectively, potentially lowering their risk in the environment due to land application. A list of compounds for which the optimized analytical method potentially can be used for detection and quantification in environmental samples is provided in the supporting document.

Effects of the origins and stabilization of biosolids and biowastes on their phosphorous composition and extractability

Phosphorous dissolution and ensuing chemical redistribution of P in organic amendments (OA) were studied by applying a modified Hedley selective fractionation to eight water-extracted and unextracted OAs. Nine 7-day, repeated extractions were applied using a 60:1 water:dry OA (v:w) ratio at pH 8. Eight OAs were tested including five biosolids, broiler litter, dairy manure compost and municipal solid waste compost. The average PWEP9 (percent water-extractable P following nine water-extraction cycles) for the OAs was 65 ± 9% and all of the fractions, with almost no exceptions, contributed to that figure. Organic P was depleted by mineralization (in non-stabilized sludges and broiler litter) or dissolution (stabilized composts) or both (in lime-treated biosolids) and that depletion was completed within 1–2 extraction cycles. Only the organic P of the MSWC remained undepleted. Strong linear correlations were observed between the WEP9 values of the OAs (0.8–21 g P kg−1) and several more easily determined properties, including total P content (r2 = 0.84), organic N content (r2 = 0.82), the sum of Hedley’s more easily dissolved SRP (soluble reactive P) and OP (r2 = 0.95), and the total P and SRP extracted by 16 h of shaking with the bicarbonate reagent (r2 ≥ 0.90). These findings indicate that if greater P availability is desired, the stabilization of biosolids and biowastes should be minimized. These insights into the relationships between OA characteristics and P solubility may benefit the use of OAs in agricultural systems and aid assessments of the environmental significance of their use.

Sulfur-aided composting facilitates ammonia release mitigation, endocrine disrupting chemicals degradation and biosolids stabilization

In order to investigate the potential effect of sulfur (S) aided composting on NH3 volatilization mitigation, bisphenol A (PBA) and estrogens (estrone, 17β-estradiol, estriol, and 17a-ethinylestradiol) degradation and biosolids stabilization, five treatments of S (i.e., 0, 0.25%, 0.50%, 1.0%, and 2.0%, dry weight basis) were applied to the mixtures of biosolids and wheat straw during the 50 days of composting stabilization process. Results implicated addition of S decreased alkalinity of compost system, mitigated NH3 volatilization, facilitated degradation of bisphenol A and estrogen in biosolids, and improved biosolids stabilization. Compared to control, the S-added treatments reduced nitrogen loss by 29.39%–97.22%, and degraded PBA and estrogens in biosolids by 25.42–72.63% and 21.11–68.14%, respectively, with S additions in range of 0.25–2.0%. In terms of economic efficiency and ecological risk, S addition at ≤0.50% is suggested for composting stabilization of biosolids.

Biosolid stabilization through dielectric barrier discharge reactor

The model simulates the air flow and temperature ina dielectric barrier discharge reactor, opening doors for biosolid stabilization research.

Macroscopic modeling of plasma effects on heat and fluid flow in a dielectric barrier discharge based process for biosolid stabilization

This work presents a simple, easily applicable macroscopic model for the simulation of the plasma effect on the fluid flow and the heat transfer, in a Dielectric Barrier Discharge (DBD) reactor used for environmental applications, such as soil remediation and biosolid stabilization. The model uses inputs that are easy to obtain experimentally, such as the inlet flow rate, electric power consumption, and reduction in the moisture of the treated specimen, in order to provide information on features that are difficult to measure, such as the temperature distribution in the plasma region and inside the specimen. The model is presented here through the simulation of a floating-electrode DBD process, and the results are compared with experimental data. For the simulation, the reactor’s exact geometry is reconstructed in the computational domain, conjugate heat transfer is considered between the flowing air and the solid components, and the treated biosolid is modeled as a porous material. The findings show that, within the selected operating window, the temperature increase in the plasma area and inside the biosolid does not exceed 100 K. Such information is crucial for the assessment of the physicochemical modification of the specimen under treatment and the suitability of the treatment procedure for targeted applications.

Review of the effects of wastewater biosolids stabilization processes on odor emissions

Odor emissions from biosolids limit opportunities for their beneficial reuse by land application. Odorous emissions are affected by the operation of stabilization processes via methods such as anaerobic digestion, aerobic digestion, alkaline treatment, thermal drying, or composting. Commonly used sampling and measurement methods for assessing odor emissions were identified and key odorants reported for biosolids produced using different stabilization methods. Generally, dominant odorants from biosolids were volatile sulfur compounds; however other odorants such as trimethylamine, ammonia, indole, p-cresol and pinene may also be sensorially important in different types of stabilized biosolids. Therefore, initial studies should target a range of odorants potentially emitted at different sites. The use of sensory analysis, which was limited in many studies, coupled with analytical methods can be effectively used to characterize nuisance emissions. The processing of the biosolids both before and after stabilization was shown in many studies to affect the resultant biosolids odorous emissions. These findings suggest that not only should the operational performance of biosolids processing before, during and after stabilization should be reported but that the biosolids management systems should consider the whole biosolids processing train, rather than just the operation of the chosen stabilization method.

Correlation Between Levels of Humic Acid and Fecal Indicator Bacteria: A Potential Predictor of Biosolids Stabilization

Abstract For safe land application, biosolids are stabilized and treated to reduce pathogen levels. Fecal indicator levels are usually measured with culture-based methods, which are time consuming and laborious. Thus, there is a need for alternative indicators that could expedite the classification of biosolids. This could be accomplished through the quantification of humic acids (HAs) as a surrogate, since the natural degradation of organic matter simultaneously breaks down and mineralizes, while also synthesizing humus, which includes the stable polyphenolics humic and fulvic acids and humin. Therefore, this study aimed to investigate whether HAs and fecal bacteria exhibit an inverse correlation, supporting the notion that the level of HAs could potentially serve as an indicator for stabilized biosolids. This entailed using laboratory-scale anaerobic digesters at two temperatures (25°C and 37°C), with levels of pathogenic (Salmonella spp.) and fecal indicator bacteria (Escherichia coli, Enterococci, and...

Investigation of the role of flocculation conditions in recuperative thickening on dewatering performance and biogas production

ABSTRACTThere is considerable interest in recuperative thickening (RT), the recycling of partially digested solids in an anaerobic digester outlet stream back into the incoming feed, as a ‘high-performance’ process to increase biogas production, increase system capacity, and improve biosolids stabilization. While polymer flocculation is commonly used in full-scale RT operations, no studies have investigated the effect of flocculation conditions on RT process performance. Our goal was to investigate the effect of polymer type and dosage conditions on dewatering performance and biogas production in a lab-scale RT system. The type of polymer flocculant significantly affected dewatering performance. For example, the 440 LH polymer (low molecular weight (MW) polyacrylamide) demonstrated lower capillary suction time (CST) and filtrate total suspended solids (TSS) values than the C-6267 polymer (high MW polyacrylamide). An examination of the dewatering performance of RT digesters with different polymers found a strong correlation between CST and filtrate TSS. The type of polymer flocculant had no significant effect on biogas productivity or composition; the methane content was greater than 60% in good agreement with typical results. The optimization of the polymer flocculation conditions is a critical task for which the lab-scale RT system used in this work is ideally suited.

Mineralizable carbon in biosolids/fly ash/sugar beet lime treated soil under field conditions

Fly ash (FA) from coal burning power plants is generally used for biosolids stabilization to reduce numbers of pathogens and availabilities of heavy metals contained in biosolids. The objective of this study was to determine the suitability of sugar beet lime (SBL) from sugar beet processing factories as fly ash substitute. Post-harvest soil samples were employed in a 180d incubation study for each of two year field experiments. A first order logistic model was used to estimate sizes of labile and delayed logistic C pools. All treatments with one exception significantly (P<0.05) reduced plant biomass compared to the mineral fertilization treatment in the first year under maximum water stress conditions. However, biosolids (7.5Mgha−1), biosolids+FA (7.5Mgha−1), and biosolids+SBL (7.5Mgha−1) significantly (P<0.05) raised plant biomass compared to the mineral fertilization in the second year under minimum water stress. Applications of biosolids together with either FA (7.5 and 15Mgha−1) or SBL (7.5 and 15Mgha−1) significantly (P<0.05) increased sizes of labile and delayed logistic pools in the first year, but they did not in the second year. The sizes of potentially mineralizable carbon pools were bigger in the second year probably due to increased accumulation of wheat root biomass originating from enhanced soil water regime. Carbon mineralization in soils treated with biosolid/fly ash/sugar beet lime at agronomic application rates depends also on plant biomass accumulation, which affects total root biomass and rhizodeposition. Sugar beet lime containing 70% CaO and 5% organic carbon seems to be a good biosolids stabilizing agent compared to fly ash in terms of plant biomass accumulation and mineralizable carbon.

Improved Biosolids Stabilization Utilizing Temperature Phased Anaerobic Digestion

Improved Biosolids Stabilization Utilizing Temperature Phased Anaerobic Digestion

Characterization of biosolids and evaluating the effectiveness of plastic-covered sun drying beds as a biosolids stabilization method in Lusaka, Zambia

Introduction The Lusaka Water and Sewerage Company (LWSC) produces *800–1,000 kg of treated sewage sludge per day at its Manchinchi wastewater treatment plant (WWTP). The biosolids are used for land application purposes although the contaminant and pathogen composition and quality of the biosolids have been unknown until this study. Zambia does not have legal standards and guidelines for biosolids management or application. The Manchinchi plant in Lusaka suffers from constant breakdowns such that the effectiveness of the plant to produce quality grade biosolids for land application use is questionable. In peri-urban areas, the problem of poor sanitation is being addressed using different technologies including urine diversion ecosan toilets. The effectiveness of ecosan toilets to stabilize faecal sludge has not been assessed in Zambia. The purpose of this study was to stabilize and characterize the biosolids from Manchinchi plant and ecosan toilets. Stabilization was done by use of drying beds and irradiation. The parametres that were used for characterization were microbiological, parasitological and heavy metals. Results Biosolids from the Manchinchi WWTP sun drying bed, ecosan toilets and from an experimental plasticcovered drying bed were found to contain different pathogenic microorganisms and contaminant levels. A radiation dose and time-related declining trend in pathogens loads in biosolids were observed. By the third week, no viable Ascaris eggs were detected. Based on controlled conditions, the biosolids quality was found to be within the internationally acceptable standards for restricted use. Conclusions Both the untreated LWSC biosolids and ecosan sludge contained pathogen levels with the potential to cause environmental and public health hazards if used for agriculture purposes. Under plastic-covered drying beds, viable Ascaris eggs were not detected by the fourth week of treatment and the biosolids were stabilized to levels equivalent to Class C of the Australian standards for restricted land application. Covered drying beds can be considered as cost effective stabilization treatment technology for biosolids in developing countries. The technology has potential benefits for improving public health and reducing environmental pollution in Zambia, especially during the rainy season when biosolids are directly discharged into the environment.

Stabilization of Sewage Sludge by Using Various By-products: Effects on Soil Properties, Biomass Production, and Bioavailability of Copper and Zinc

Stabilization of sewage sludge (SS) prior to its land disposal may help control the mobility of SS-borne contaminants, particularly potentially toxic metals. We examined the effects of stabilized SS application on soil properties, biomass production, and phytoavailability of Cu and Zn to plants grown in two contrasting soils, Entisol and Aridisol. Stabilized SS mixtures were created by mixing SS in a 3-to-1 ratio with bentonite (B), sugar beet factory lime (SL), brick factory fly ash (BFA), rice straw (RS), water hyacinth (WH), and 50:50 mixture of RS and SL. Mixtures were applied at 50 Mg ha−1, and Sorghum vulgare L. and Eurica sativa were grown in a pot experiment. All the amendments increased plant availability and uptake of both Cu and Zn compared to the unamended control. The application of stabilized SS increased dry plant biomass significantly and decreased DTPA-extractable elements compared to the non-stabilized SS treatment. We conclude that of the six amendments studied, especially sugar beet factory lime (SL) and bentonite (B), are promising for the stabilization of metal-contaminated biosolids and should be tested under field conditions.

Macromolecular Products from Biosolids and its Morphologic Change Employing Hydrothermal Treatment

Hydrothermal treatment is a benefit process for the mass reduction, stabilization and recycling of biosolids, however, the mutual relation between mass transfer and physicochemical property are still unclear. Our work undertook the hydrothermal treatment of biosolids in batch reactors under different temperature ranged from 180-300°C. Result showed that protein and carbohydrate were the primary macromolecular compounds in initial hydrothermal reaction, and protein was richer but less stable than carbohydrate. Temperature is a key factor affecting the organic matter transferring process between solid and liquid phase, reaction efficiency markedly reduced when temperature drop to 180°C. Morphologic change of biosolids was observed, including a rapid dewatering process in initial reaction and disintegration process to small size particles.