Ultrafiltration fractionation of potentially inhibitory substances of hydrothermal liquefaction aqueous phase derived from municipal sludge.

Hydrothermal liquefaction (HTL) is a promising thermo-chemical technology for municipal sludge treatment due to its potential for biocrude oil recovery and minimizing biosolids management costs. However, the process generates a high volume of an aqueous byproduct that needs to be treated due to its high chemical oxygen demand (COD) and various organic and inorganic compounds. Although the aqueous phase is known to contain recalcitrant and potentially inhibitory substances that may affect its biological treatment, their molecular weight distribution (MwD) and its impact on anaerobic biodegradability are poorly understood. Ultrafiltration (UF) was conducted to fractionate HTL aqueous into different molecular weight (Mw) fractions using 300, 100, 10, and 1 kDa membranes. Mesophilic biochemical methane potential (BMP) assays were conducted to assess the anaerobic biodegradability of each fraction, and the first-order model was used to calculate the degradation kinetics of potential inhibitory compounds. The highest percentage of organics (65 %) was found in the Mw<1 kDa range, whereas the 10>Mw>1 kDa had the lowest percentage (8 %). There was no significant difference in the cumulative specific methane produced from various Mw fractions (p>0.05). The Mw<1 kDa fraction had the highest first-order specific methane production rate (0.53 day-1), whereas the unfiltered HTL had the lowest (0.38 day-1). Although UF fractionation increased the rate of anaerobic degradation of HTL aqueous for the Mw<1 kDa fraction, the observed methane potential was only 55 % of the theoretical value. This implies that 45 % of COD remains undegraded even after permeation through the lowest Mw cut-off membrane. Therefore, further characterization of HTL aqueous is needed for compounds with molecular weights below 1 kDa to fully understand the nature of inhibitory organics and their impact on anaerobic digestion. Furthermore, pretreatments utilizing techniques such as adsorption and advanced oxidation may be necessary to enhance the specific methane yields from various HTL aqueous fractions, thereby bringing them closer to the theoretical yield.

Effects of municipal sludge composition on hydrothermal liquefaction products: Aqueous phase characterization and biodegradability assessment.

Hydrothermal liquefaction (HTL) aqueous phases derived from mixed sludge and digested sludge of two wastewater treatment plants (WWTP) were characterized considering variations in primary-secondary sludge ratios, an aspect previously overlooked in the literature. Mixed sludge was obtained by mixing primary and secondary sludge to simulate high primary sludge, average, and high secondary sludge cases. Aerobic and mesophilic/thermophilic anaerobic biodegradability tests were conducted. Higher chemical oxygen demand, total ammonium-N, orthophosphate-P, fatty acids, and N-heterocycles in HTL aqueous samples were detected as the secondary sludge ratio increased in mixed sludge. A similar trend was observed in the biodegradability tests. Characteristics of HTL aqueous derived from mixed sludge of WWTP 1 showed much higher variation, whereas WWTP 2 mixed sludge was not affected significantly by primary-secondary sludge ratios. Finally, the biodegradability levels of HTL aqueous samples were determined to be 69-78 % under aerobic, 58-70 % under mesophilic anaerobic, and 42-56 % under thermophilic anaerobic conditions.

Treatment of aqueous phase from hydrothermal liquefaction of municipal sludge by adsorption: Comparison of biochar, hydrochar, and granular activated carbon.

Hydrothermal liquefaction (HTL) is promising for treating waste with high moisture, such as municipal sludge, and producing biocrude (a petroleum-like biofuel). However, a large amount of wastewater byproduct, HTL aqueous, is generated. The presence of hazardous compounds (e.g., phenolic compounds and nitrogenous organics) makes HTL aqueous the biggest bottleneck for full-scale implementation at treatment plants. This study investigated the adsorption of various pollutants, focusing on chemical oxygen demand (COD), in HTL aqueous to granular activated carbon (GAC), biochar, and hydrochar. It assessed the effect of pH, temperature, time, and adsorbent concentration on adsorption efficiency and identified proper adsorbent and process conditions for removing most of the pollutants from HTL aqueous. GAC showed the highest adsorption capacity (184 mg/g) for COD, surpassing biochar (44 mg/g) and hydrochar (42 mg/g). The adsorption of COD to all adsorbents followed pseudo-second-order kinetic and Freundlich isotherm, suggesting that the adsorption of HTL aqueous pollutants is a heterogeneous and multilayer process, limited by chemosorption. The adsorption was endothermic, favored by elevated temperatures and neutral pH. This means adsorption is more efficient and economical for treating HTL aqueous that is a hot stream at the large-scale and it saves chemical needs. Lastly, GAC was highly efficient and selective in removing harmful pollutants, such as COD (up to 66%), total phenolic compounds (up to 94%), pyrazines (up to 99%), pyridines (up to 100%), and cyclic ketones (up to 95%) while preserving valuable volatile fatty acids (VFAs) and ammonia for subsequent recovery. Removal of potentially inhibitory compounds and preserving VFAs are crucial for carbon recovery in anaerobic biological treatment of HTL aqueous. The results suggested the necessity of optimizing adsorbent dose for maximizing removal of specific group of inhibitory compounds in full-strength HTL aqueous for enhancing downstream biological treatment. Lastly, this study established the groundwork for HTL aqueous adsorption, elucidating its effectiveness and mechanism for pollutant removal.

Characterization of the Mechanical, Biodegradation, and Morphological Properties of NBR/Biopolymer Blend, Integrated with a Risk Evaluation.

Biopolymer blends have attracted considerable attention in industrial applications due to their notable mechanical properties and biodegradability. This work delves into the innovative combination of butadiene-acrylonitrile (referred to as NBR) with a pectin-based biopolymer (NGP) at a 90:10 mass ratio through a detailed analysis employing mechanical characterization, Fourier transform infrared (FTIR) analysis, thermogravimetric analysis (TGA), and morphology studies using SEM. Additionally, biopolymer's biodegradability under aerobic and anaerobic conditions is tested. The study's findings underscore the superior tensile strength and elongation at break of the NGP/NBR blend in comparison to pure NBR, while also exhibiting a decrease in puncture resistance due to imperfect bonds at the particle-matrix interfaces, necessitating the use of a compatibilizer. In anaerobic conditions, evaluation of biodegradable properties reveals 2% and 12% biodegradability in NBR and NGP/NBR blend, respectively. The degradation properties were also aligned with TGA results highlighting a lower decomposition temperature for NGP. Additionally, this research integrates the application of a conditional value-at-risk (CVaR)-based analysis of the blend's tensile properties to evaluate the uncertainty impact in the experiment. Under risk, a significant enhancement in the tensile performance (by 80%) of the NGP/NBR blend was shown compared to pure NBR. Ultimately, the study shows that adding pectin to the NBR compound amplifies the overall performance of the biopolymer significantly under select criteria.

Evaluation of on-site biological treatment options for hydrothermal liquefaction aqueous phase derived from sludge in municipal wastewater treatment plants.

Aerobic treatment, mesophilic anaerobic digestion, thermophilic anaerobic digestion, and dark fermentation were evaluated for on-site biological treatment of municipal sludge derived HTL aqueous. For all four described batch test scenarios, municipal sludge-derived HTL aqueous samples obtained under 290-360 °C and 0-30 min retention time were used. In the aerobic respirometric tests, HTL aqueous samples resulted in a five-day biochemical oxygen demand range of 40.75 g/L (350 °C-25.6 min) to 54 g/L (325 °C-0 min). The calculated aerobic biodegradability index showed that approximately 50 % of the organics in HTL aqueous were easily biodegradable. Mesophilic and thermophilic biochemical methane potential tests resulted in specific yields of 151-179 mL CH4/g chemical oxygen demand (COD) and 103-122 mL CH4/g COD, respectively. HTL aqueous obtained under 360 °C-15 min condition caused total inhibition in both mesophilic and thermophilic anaerobic digestion. Possible causes for this inhibition were pyridine, pyrrolidinone, piperidinone, pyridinol, and phenolic compounds, which were higher in abundance in the 360 °C-15 min sample. HTL aqueous was found unfit for hydrogen production in dark fermentation due to inhibitory composition. In summary, on-site biological treatment of HTL aqueous was found to be most suitable under aerobic and mesophilic anaerobic conditions.

Phosphorus recovery from municipal sludge-derived hydrochar: Insights into leaching mechanisms and hydroxyapatite synthesis.

Hydrothermal liquefaction has the potential to exploit resources from municipal sewage sludge. It converts most organics into a liquid biofuel (biocrude), concentrates P in the solid residue (hydrochar), and consequently enables its efficient recovery. This study thoroughly evaluated the effects of extraction conditions on P and metal release from hydrochar by nitric acid. Among assessed factors, acid normality (0.02-1 N), liquid-to-solid ratio (5-100 mL/g), and contact time (0-24 h) had positive effects while decreasing eluate pH (0.5-4) improved leaching efficiencies of P and metals. Notably, eluate pH played a dominant role in P leaching and pH < 1.5 was crucial for complete extraction. P and metal leaching from hydrochar have strong interactions and their leaching mechanism was identified as product layer diffusion using the shrinking core model. This suggests that the leaching efficiency is susceptible to agitation and particle size but not temperature. Using 10 mL/g of 0.6 N HNO3 for 2 h was considered the best extraction condition for efficient P leaching (nearly 100%) and minimization of cost and contaminants (heavy metals). Following extraction, adding Ca(OH)2 at a Ca:P molar ratio of 1.7-2 precipitated most P (99-100%) at pH 5-6, while a higher pH (13) synthesized hydroxyapatite. The recovered precipitates had high plant availability (61-100%) of P and satisfactory concentrations of heavy metals as fertilizers in Canada and the US. Overall, this study established reproducible procedures for P recovery from hydrochar and advanced one step closer to wastewater biorefinery.

An improved plastination method for strengthening bamboo culms, without compromising biodegradability.

Biomaterials are increasingly being designed and adapted to a wide range of structural applications, owing to their superior mechanical property-to-weight ratios, low cost, biodegradability, and CO2 capture. Bamboo, specifically, has an interesting anatomy with long tube-like vessels present in its microstructure, which can be exploited to improve its mechanical properties for structural applications. By filling these vessels with a resin, e.g. an applied external loading would be better distributed in the structure. One recent method of impregnating the bamboo is plastination, which was originally developed for preserving human remains. However, the original plastination process was found to be slow for bamboo impregnation application, while being also rather complicated/methodical for industrial adaptation. Accordingly, in this study, an improved plastination method was developed that is 40% faster and simpler than the original method. It also resulted in a 400% increase in open-vessel impregnation, as revealed by Micro-X-ray Computed Tomography imaging. The improved method involves three steps: acetone dehydration at room temperature, forced polymer impregnation with a single pressure drop to - 23 inHg, and polymer curing at 130 °C for 20 min. Bamboo plastinated using the new method was 60% stronger flexurally, while maintaining the same modulus of elasticity, as compared to the virgin bamboo. Most critically, it also maintained its biodegradability from cellulolytic enzymes after plastination, as measured by a respirometric technique. Fourier transform infrared-attenuated total reflection, and thermogravimetric analyses were conducted and showed that the plastinated bamboo's functional groups were not altered significantly during the process, possibly explaining the biodegradability. Finally, using cone calorimetry, plastinated bamboo showed a faster ignition time, due to the addition of silicone, but a lower carbon monoxide yield. These results are deemed as a promising step forward for further improvement and application of this highly abundant natural fiber in engineering structures.

Biochar and wood ash amended anaerobic digestion of hydrothermally pretreated lignocellulosic biomass for biorefinery applications.

This study investigated the effect of biochar and wood ash amendment on the anaerobic digestion of hydrothermally pretreated lignocellulosic biomass. Hydrothermal pretreatment was performed on switchgrass at 200, 250, and 300 °C with 0, 30, and 60 min of retention times. The pretreatment method was optimized using the response surface method for enhanced methane production. At the optimum pretreatment (200 °C/0 min retention time), a specific methane yield of 256.9 mL CH4/g volatile solids (VS), corresponding to an increase of 32.8% with respect to the untreated substrate, was obtained. Hydrothermal pretreatment was beneficial for methane production at temperatures lower than 220 °C and retention times shorter than 20 min. At more severe pretreatment conditions than 220°-20 min, sugars were degraded into other products, causing a decrease in the methane yield. The hydrothermal degradation products, i.e., acetic acid, lactic acid, furfural, and hydroxymethylfurfural concentrations, were also measured and modeled. The addition of biochar and wood ash to BMP assays were tested at 2, 9, 16 g/g VSinoculum ratios and <63, 63-125, 125-250 µm particle sizes. A decline in methane production was observed for all tested doses and particle sizes of both additives. The decline in the methane potential was proportional to the doses and particle sizes. Kinetic modeling of BMP test results also supported that using the additives was not beneficial. Based on the result of this study, it was found that the use of biochar and wood ash in a pretreated lignocellulosic biomass processing biorefinery would not be beneficial.

Laboratory and field scale biodegradability assessment of biocomposite cellphone cases for end-of-life management.

The increase in production of biobased plastics as a replacement for fossil fuel-based plastics has created the need for studies to assess their degradation under various conditions. However, developing reliable laboratory and field-testing protocols for biobased materials and products still requires extensive research. In this study, the biodegradability of a biocomposite consumer product, smart cellphone case, was determined under laboratory scale anaerobic (38 °C) and composting assays (58 °C) as well as under field scale (60-67 °C) composting conditions. The laboratory scale composting assay was conducted for 46 days using cellphone cases with dimensions of 7 × 3.5 × 0.2 and 4.6 × 3.5 × 0.2 cm, which achieved approximately 20% biodegradation. The field scale composting conditions achieved 55% weight loss of cellphone cases in 80 days. The subsequent anaerobic biodegradation assays contained three different sized (grinded, cut into 2 × 2 × 0.2 and 4 × 4 × 0.2 cm pieces) biocomposite cellphone cases conducted under mesophilic conditions for 169 days. Among the conditions tested, the size of cellphone cases did not cause a significant difference in biodegradation under anaerobic conditions. Anaerobic digestion conditions yielded only 6-8% biodegradation, which was significantly lower than that of composting. The results agree with literature on conventional waste streams stating that aerobic microbial processes are more effective to break down complex substrates, similar to biocomposite cellphone cases tested, than their anaerobic counterparts.

Biochar amendment rapidly shifts microbial community structure with enhanced thermophilic digestion activity.

Effects of powdered (<0.075 mm) biochar on thermophilic anaerobic digestion were investigated with biochemical methane potential (BMP) assays. The assays had substrate to inoculum ratios (SIR) of 2.2 and 4.4 g-volatile solids (VS)/g-VS and biochar dosing of 6 g/g-total solids (TS)inoculum. Compared to control, biochar amendment enhanced methane production rates by 94%, 75%, and 20% in assays utilizing substrates of acidified sludge at 70 °C, 55 °C and non-acidified mixed sludge, respectively. All controls experienced acute inhibition with lag phases from 12 - 52 days at SIR of 4.4 g-VS/g-VS, while assays with biochar generated methane from day 4. Biochar addition resulted in a rapid shift in microbial community structure associated with an increase in Methanothermobacteraeae (hydrogenotrophic) and Methanosarcinaceae archaea, as well as various volatile fatty acid (VFA)-degrading and hydrogen-producing bacteria. Biochar presents great potential to tackle VFA accumulation, abbreviate lag phase and increase methane rate, particularly at high organic loadings.

Enhancement of lignocellulosic biomass anaerobic digestion by optimized mild alkaline hydrogen peroxide pretreatment for biorefinery applications.

Lignocellulosic energy crops are promising feedstocks for producing renewable fuels, such as methane, that can replace diminishing fossil fuels. However, there is a major handicap in using lignocellulosic sources to produce biofuels, which is their low biodegradability. In this study, the application and the optimization of a lignocellulose pretreatment process, named alkaline hydrogen peroxide, was investigated for the enhancement of methane production from the energy crop switchgrass. Four independent process variables, solid content (3-7%), reaction temperature (50-100 °C), H2O2 concentration (1-3%), and reaction time (6-24 h), and three response variables, soluble reducing sugar, soluble chemical oxygen demand, and biochemical methane potential were used in process optimization and modeling. The optimization was performed by two different approaches as maximum methane production and cost minimization. The optimum conditions for the highest methane production were found as 6.65 wt% solid content, 50.6 °C reaction temperature, 2.94 wt% H2O2 concentration, and 16.05 h reaction time. The conditions providing the lowest cost were 6.43 wt% solid content, 50 °C reaction temperature, 1.83 wt% H2O2 concentration, and 6.78 h reaction time. For maximum methane production and cost minimization, specific methane yields of 338.52 mL CH4/g VS and 291.34 mL CH4/g VS were predicted with 62.4 % and 39.8 % enhancements compared to untreated switchgrass, respectively. Finally, it was found that the predicted methane production for the maximum methane production represents 77 % of the theoretical methane yield and 82.22 % energy recovery.

Examination of single-stage anaerobic and anoxic/aerobic and dual-stage anaerobic-anoxic/aerobic digestion to remove pharmaceuticals from municipal biosolids.

Many trace contaminants of emerging concern (CECs) including a number of pharmaceutically active compounds are not effectively removed during conventional wastewater treatment processes and instead accumulate in wastewater sludge. Unfortunately, many existing sludge stabilization treatments such as anaerobic digestion (AD) also have limited effectiveness against many of these CECs including the four pharmaceuticals ibuprofen, diclofenac, carbamazepine, and azithromycin which can then enter the environment through the disposal or land application of biosolids. Single-stage AD, single-stage cycling aerobic-anoxic (AERO/ANOX) and sequential digesters (AD followed by an AERO/ANOX digester) at sludge retention times (SRT) of 5 to 20-days were evaluated side-by-side to assess their effectiveness in removing pharmaceuticals and conventional organic matter. Single-stage ADs (35 °C) and AERO/ANOX (22 °C) digesters effectively removed total solids while sequential AD + AERO/ANOX digesters offered further improvements. Ibuprofen was not effectively removed during AD and resulted in up to a 23 ± 8% accumulation. However, ibuprofen was completely removed during AERO/ANOX digestion and in several sequential digestion scenarios. Each type of digestion was less effective against carbamazepine with slight (3 ± 2%) accumulations to low levels (14 ± 1%) of removals in each type of digestion studied. Diclofenac was more effectively removed with up 30 ± 3% to 39 ± 4% reductions in the single-stage digesters (AD and AERO/ANOX, respectively). While sequential digestion scenarios with the longest aerobic SRTs significantly increased diclofenac removals from their first-stage digesters, scenarios with the longest anaerobic SRTs actually decreased removals from first-stage digesters, possibly due to reversible biotransformation of diclofenac conjugates/metabolites. Up to 43 ± 6% of azithromycin was removed in AERO/ANOX digesters, while the best performing sequential-digester scenario removed up to 63 ± 7% of azithromycin. This study shows that different digester configurations can reduce the CEC burden in biosolids while also greatly reducing their volumes for disposal, although none can remove CECs completely.

Hydrochar derived from municipal sludge through hydrothermal processing: A critical review on its formation, characterization, and valorization.

Additional options for the sustainable treatment of municipal sludge are required due to the significant amounts of sludge, high levels of nutrients (e.g., C, N, and P), and trace constituents it contains. Hydrothermal processing of municipal sludge has recently been recognized as a promising technology to efficiently reduce waste volume, recover bioenergy, destroy organic contaminants, and eliminate pathogens. However, a considerable amount of solid residue, called hydrochar, could remain after hydrothermal treatment. This hydrochar can contain abundant amounts of energy (with a higher heating value up to 24 MJ/kg, dry basis), nutrients, and trace elements, as well as surface functional groups. The valorization of sludge-derived hydrochar can facilitate the development and application of hydrothermal technologies. This review summarizes the formation pathways from municipal sludge to hydrochar, specifically, the impact of hydrothermal conditions on reaction mechanisms and product distribution. Moreover, this study comprehensively encapsulates the described characteristics of hydrochar produced under a wide range of conditions: Yield, energy density, physicochemical properties, elemental distribution, contaminants of concern, surface functionality, and morphology. More importantly, this review compares and evaluates the current state of applications of hydrochar: Energy production, agricultural application, adsorption, heterogeneous catalysis, and nutrient recovery. Ultimately, along with the identified challenges and prospects of valorization approaches for sludge-derived hydrochar, conceptual designs of sustainable municipal sludge management are proposed.

Anaerobic co-digestion of oil-extracted spent coffee grounds with various wastes: Experimental and kinetic modeling studies.

The effect of oil extraction from spent coffee grounds as a pre-treatment strategy prior to anaerobic digestion besides assessing the feasibility of defatted spent coffee grounds co-digestion with spent tea waste, glycerin, and macroalgae were examined. Mesophilic BMP tests were performed using defatted spent coffee grounds alongside four co-substrates in the ratio of 25, 50, and 75%, respectively. The highest methane yield was obtained with the mono-digestion of defatted spent coffee grounds with 336 ± 7 mL CH4/g VS and the yield increased with the increase in the mass ratio of defatted spent coffee grounds during co-digestion. Moreover, defatted spent coffee grounds showed the highest VS and TS removal at 35.5% and 32.1%, respectively and decreased thereafter. Finally, a linear regression model for the interaction effects between substrates was demonstrated and showed that distinctly mixing defatted spent coffee grounds, spent coffee grounds, and spent tea waste outperforms other triple mixed substrates.

Comparative response of thermophilic and mesophilic sludge digesters to zinc oxide nanoparticles.

The inevitable discharge of zinc oxide nanoparticles (ZnO NPs), from consumer and industrial products, into wastewater treatment plants (WWTPs) has created a need to determine their effect on sludge digestion. In this study, the effect of particle size (30 nm and 100 nm), type (coated and non-coated), and dose (6, 75, and 150 mg/g feed total solids (TS)) of ZnO NPs on anaerobic sludge digestion was studied under mesophilic (35 °C) and thermophilic (55 °C) conditions. The effect was investigated in two stages with different digester feeding regime: (1) batch biochemical methane potential (BMP) assays, and (2) semi-continuously fed reactors. Results showed that ZnO NPs were inhibitory at medium and high levels (75 and 100 mg ZnO/g TS, respectively). Coated NPs created less inhibition than non-coated NPs. Thermophilic bacteria were more sensitive to ZnO NPs compared with mesophilic bacteria. For the non-coated ZnO NPs, only the mesophilic batch assays were able to recover at the medium concentration and the thermophilic reactors presented chronic inhibition and could not recover. As a beneficial outcome, coated ZnO NPs significantly reduced odor-causing volatile sulfur compounds in digester headspace in comparison with the non-coated NPs. In summary, the condition in which ZnO NPs would have little to no effect would be 6 mg/g TS-coated ZnO NPs under mesophilic conditions.

A Review on the Fate of Legacy and Alternative Antimicrobials and Their Metabolites during Wastewater and Sludge Treatment.

Antimicrobial compounds are used in a broad range of personal care, consumer and healthcare products and are frequently encountered in modern life. The use of these compounds is being reexamined as their safety, effectiveness and necessity are increasingly being questioned by regulators and consumers alike. Wastewater often contains significant amounts of these chemicals, much of which ends up being released into the environment as existing wastewater and sludge treatment processes are simply not designed to treat many of these contaminants. Furthermore, many biotic and abiotic processes during wastewater treatment can generate significant quantities of potentially toxic and persistent antimicrobial metabolites and byproducts, many of which may be even more concerning than their parent antimicrobials. This review article explores the occurrence and fate of two of the most common legacy antimicrobials, triclosan and triclocarban, their metabolites/byproducts during wastewater and sludge treatment and their potential impacts on the environment. This article also explores the fate and transformation of emerging alternative antimicrobials and addresses some of the growing concerns regarding these compounds. This is becoming increasingly important as consumers and regulators alike shift away from legacy antimicrobials to alternative chemicals which may have similar environmental and human health concerns.

Comparison of anaerobic, cycling aerobic/anoxic, and sequential anaerobic/aerobic/anoxic digestion to remove triclosan and triclosan metabolites from municipal biosolids.

The antimicrobial triclosan (TCS) is a pervasive and persistent environmental micropollutant which can contaminate land, biota, and water through the land application of biosolids. Many existing sludge management techniques have limited effectiveness against TCS and TCS metabolites including triclosan-sulfate (TCS-SO4). The objective of this study was to evaluate the impacts of different digestion types (anaerobic, aerobic/anoxic, and sequential anaerobic + aerobic/anoxic), temperatures, and digester sludge retention times (SRTs) on the destruction of organic matter, and on TCS/TCS metabolites. Conventional mesophilic anaerobic digesters (AD), room temperature cycling aerobic/anoxic digesters (AERO/ANOX), and sequential AD + AERO/ANOX digesters were all effective in removing organic matter. The optimum single-stage AD, and AERO/ANOX scenarios were both 20-day SRTs which had 52.3 ± 1.4 and 47.1 ± 3.7% chemical oxygen demand (COD) removals, respectively. Sequential AD + AERO/ANOX digesters improved organic matter destruction, removing up to 68.2 ± 2.1% of COD at an 8-day AD + 12-day AERO/ANOX second-stage (mesophilic) SRTs. While AD showed modest levels of TCS removals (all <40%), TCS was substantially more degradable aerobically with AERO/ANOX removing up to 80.3 ± 2.5% of TCS and nearly all TCS-SO4 entering the digester at a 20-day SRT. Sequential AD + AERO/ANOX removed virtually all TCS-SO4 entering the system and improved TCS removals from first stage ADs. However, they were less effective than a single-stage AERO/ANOX digester operating at the same overall SRT. These results demonstrate that AERO/ANOX and sequential AD + AERO/ANOX processes could be used to reduce the amount of TCS, TCS-SO4 and TCS-related compounds in digested sludge, minimizing the environmental burden of the land application of biosolids.

Mitigation of recalcitrant nutrients and organic pollutants from small- to medium-scale biological nutrient removal plant sludge by digester optimization.

Digestion of biological nutrient removal (BNR) plant sludge can be challenging, particularly for small- to medium-sized wastewater treatment facilities (WWTF) which often lack the economies of scale, and/or expertise to make digestion feasible. This study compared various types of sludge digestion, sludge retention times (SRTs), and temperatures on the release of recalcitrant nutrients, digestion economics, and digester performance utilizing mixed primary and secondary sludge from a small- to medium-sized BNR facility. Mesophilic anaerobic digestion (AD), cycling aerobic/anoxic (AERO/ANOX) digestion, and sequential anaerobic/aerobic/anoxic (AD/AERO/ANOX) digestion at room and mesophilic temperatures were compared at SRTs between 5 and 20 days. AERO/ANOX digestion was very effective in treating recalcitrant forms of nitrogen and phosphorous by removing up to 87% of dissolved organic nitrogen (DON), up to 88 ± 2% of non-reactive dissolved phosphorous (NRDP). AERO/ANOX digestion also offered the lowest increase in sludge management costs versus the existing no-digestion baseline scenario. ADs removed up to 53 ± 1% of volatile solids (VS), whereas unheated AERO/ANOX digesters were less effective, removing up to 39 ± 1% of VS. Sequential AD/AERO/ANOX digesters with a mesophilic second-stage removed up to 61 ± 3% of VS but had the highest operational and capital costs. Experiments also indicated that significant amounts of orthophosphate (PO43-) may be released from digested AERO/ANOX sludge during on-site storage, with longer SRTs releasing PO43- more rapidly than shorter ones. These results are important as more WWTFs deploy BNR to meet increasingly stringent nutrient limits.

Occurrence of the Persistent Antimicrobial Triclosan in Microwave Pretreated and Anaerobically Digested Municipal Sludges under Various Process Conditions.

Treatment of emerging contaminants, such as antimicrobials, has become a priority topic for environmental protection. As a persistent, toxic, and bioaccumulative antimicrobial, the accumulation of triclosan (TCS) in wastewater sludge is creating a potential risk to human and ecosystem health via the agricultural use of biosolids. The impact of microwave (MW) pretreatment on TCS levels in municipal sludge is unknown. This study, for the first time, evaluated how MW pretreatment (80 and 160 °C) itself and together with anaerobic digestion (AD) under various sludge retention times (SRTs: 20, 12, and 6 days) and temperatures (35 and 55 °C) can affect the levels of TCS in municipal sludge. TCS and its potential transformation products were analyzed with ultra-high-performance liquid chromatography and tandem mass spectrometry. Significantly higher TCS concentrations were detected in sludge sampled from the plant in colder compared to those in warmer temperatures. MW temperature did not have a discernible impact on TCS reduction from undigested sludge. However, AD studies indicated that compared to controls (no pretreatment), MW irradiation could make TCS more amenable to biodegradation (up to 46%), especially at the elevated pretreatment and digester temperatures. At different SRTs studied, TCS levels in the thermophilic digesters were considerably lower than that of in the mesophilic digesters.

Effect of biochar and wood ash amendment on biochemical methane production of wastewater sludge from a temperature phase anaerobic digestion process.

Biochemical methane production (BMP) assays of acidified municipal sludge were conducted with local char (biochar and wood ash) in granular (0.85-4.75 mm) and powdered (<0.075 mm) form. The effects of char addition on BMP were investigated under high acid stress conditions at substrate to inoculum ratios of 2.2, 3.2 and 4.4 g volatile solids (VS)/g-VS and char dosages of 0.2-3.7 g/g-VSsubstrate. Powdered biochar at dosage of 0.8-3.7 g/g-VSsubstrate achieved the highest improvement in rate of methane production with 192-461% increase from controls, in the first 16 days. This increase was followed by an early stationary methane production phase and a reduction of total methane yield by up to 25%. Results indicated that the early plateau could be caused by adsorption of volatile fatty acids by the biochar.