Pretreatment Of Waste Activated Sludge Research Articles

Clarifying the mechanism of peroxydisulfate and sulfite activated by Fe2+ for waste activated sludge pretreatment: Enhancement of dewaterabiliy, removal of antibiotic resistance genes and pathogenic microorganisms

The remarkable performance of SO4•— based advanced oxidation processes in improving waste activated sludge (WAS) dewatering has recently received considerable attention. However, its potential effect on the removal of emerging pollutants is often overlooked. In this study, two types of pretreatment methods (S2O82-/Fe2+ and SO32-/Fe2+) were employed to comprehensively evaluate their performance in improving the dewatering of WAS and the removal of antibiotic resistance genes (ARGs) and pathogenic microorganisms. At the optimal dosage of 1.2/1.5 mmol-S2O82-/Fe2+/g-VS, the capillary suction time reduction rate of WAS after S2O82-/Fe2+ was 1.8 times than that of SO32-/Fe2+. Notably, both S2O82-/Fe2+ and SO32-/Fe2+ could remove the 12 types of ARGs identified in WAS. Nonetheless, S2O82-/Fe2+ was more effective in removing ARGs, with a range of removal rate (0.96–2.17 log-units), and reduced the propagation and proliferation potential of residual ARGs. Furthermore, the coliforms content in WAS after S2O82-/Fe2+ decreased significantly with a minimum of 1.84 ± 0.24 log (MPN/g-TS) compared to SO32-/Fe2+. Further analysis indicated that the redistribution of bound extracellular polymeric substances (EPS) in WAS, especially the variations in protein, was the key factor affecting the dewaterability. In contrast to SO32-/Fe2+, the S2O82-/Fe2+ could quickly destroy the EPS structure to release bound water, accelerate the dissociation of WAS flocs, and cause cell lysis and DNA dissolution because of the continuous production and accumulation of SO4•— in the hostile conditions inside. Therefore, S2O82-/Fe2+ is an efficient, economical, and green method to improve WAS dewatering and the removal of pollutants.

Innovative waste activated sludge pre-treatment using a raceway pond Reactor: Integration of Low-Temperature and solar radiation

A novel pre-treatment, using a raceway pond reactor (RPR), combining the use of thermal and solar effects, was applied to enhance anaerobic digestion (AD) of waste activated sludge (WAS) from an urban wastewater treatment plant. Thermal pre-treatment at 25, 50, 60 and 70 °C was carried out for 5 h with (under distinct values of UV radiant power) and without solar radiation and varying WAS depth in the RPR (5 or 7 cm). Higher temperatures (60 and 70 °C) and longer treatment times (3 to 5 h) resulted in increased disintegration of bacterial cells. The WAS pre-treatment significantly (p-value ≤ 0.001) boosted soluble chemical oxygen demand (SCOD) levels, achieving a disintegration degree of 19.7 % at 70 °C with solar radiation (7.2 kJUV L-1WAS), which corresponds to a 15-fold increase of SCOD, compared to the baseline at 25 °C without radiation. Moreover, at the highest temperature (70 °C), there was a significant SCOD increase (p-value ≤ 0.05) of approximately 400 mgO2 L-1 in the presence of solar radiation. This synergetic effect between temperature and solar radiation caused cell damage, membrane rupture, and release of cellular content, shifting extracellular polymeric substances from tightly bound to loosely bound and soluble fractions, consequently improving methane production. Methane production increased by 131 % compared to the control (25 °C) under 70 °C and after 7.2 kJUV L-1WAS, indicating a positive impact on WAS hydrolysis. The technology adopted in this work fosters methane production predominantly using renewable solar energy without chemical residues. This is the first report on RPR for WAS pre-treatment, combining mild temperature and solar radiation.

Development of oriented multi-enzyme strengthens waste activated sludge disintegration and anaerobic digestion: Performance, components transformation and microbial communities

Low methane production and long retention time are the main dilemmas in current anaerobic digestion (AD) of waste activated sludge (WAS). This work used WAS as only substrate to prepare oriented multi-enzyme (ME) that directly used for WAS pretreatment. Under the optimal parameters, the highest activities of protease and amylase in ME could respectively reach 16.5 U/g and 580 U/g, and the corresponding methane production attained 197 mLCH4/g VS, which was increased by 70.4% compared to blank group. It was found that ME pretreatment could strengthen WAS disintegration and organic matters dissolution, lead to the soluble chemical oxygen demand (SCOD) was increased from the initial 486 mg/L to 2583 mg/L, and the corresponding volatile suspended solid (VSS) and extracellular polymeric substances (EPS) were reduced by 27% and 73.8%, respectively. The results of three-dimensional excitation-emission matrix (3D-EEM) and Fourier transform infrared spectroscopy (FTIR) indicated that protein disintegration may be the critical step during the process of WAS hydrolysis with ME, of which the release of tyrosine-like proteins achieved the better biodegradability of WAS, while the results of X-ray photoelectron spectroscopy (XPS) showed that the formation of protein derivatives was the main harmful factor that could extend the lag phase of AD process. Microbial communities analysis further suggested that ME pretreatment facilitated the enrichment of acetogenic bacteria and acetotrophic methanogens, which caused the transition of the methanogenesis pathway from hydrogenotrophic to acetotrophic. This study is expected to furnish valuable insight for ME pretreatment on enhancing WAS disintegration and methane production.

Biogas enhancement in the anaerobic digestion of thermo-chemically pretreated sludge by stimulating direct interspecies electron transfer by biochar and graphene

It is necessary to pretreat waste-activated sludge (WAS) to disintegrate the sludge matrix and amend its anaerobic digestion (AD) with carbon-based materials (CMs) to accelerate direct interspecies electron transfer (DIET) in order to realize the maximum biogas potential of abundant and habitat-threatening organic WAS. The AD of WAS pretreated thermo-chemically at 0.5% NaOH (g/g dry sludge) and 125 °C microwave irradiation was amended by biochar doses of 0–40 g/L and graphene doses of 50–1,000 mg/L in the batch operation mode. Hybrid pretreatment of WAS deteriorated dewaterability but solubilized 38% of total chemical oxygen demand (COD). AD amended with 20 g/L biochar and 100 mg/L graphene had the optimum accumulative methane yield of 183.6 and 153.8 mL/gVS, respectively, which correspond to 42.8% and 24.8% increases compared to an unamended control assay with maximum methane content of 70.3% and 71.9%, respectively. The digestate of biochar- and graphene-amended assays resulted in higher TS% and alkalinity, reduced sCOD, VFA, and turbidity, and increased particle size distribution compared to control. Biochar-amended digestate had improved dewaterability, while digestate of graphene-amended assays resulted in worse dewaterability than control. The t-test showed a significant difference between the biochar and graphene amended batch assays, while principal component analysis (PCA) indicated that biogas yield was closely correlated with pH. CM-amended batch assays demonstrated superb fitting with modified Gompertz, logistic, and first-order models with a coefficient of determination above 0.97. Microbial community abundance and diversity were affected by CMs amendment, resulting in increased acetoclastic methanogen growth and transformed methanogenic metabolic pathways. An extended pilot-scale study and techno-economic and life cycle assessments are required to investigate environmental impacts and feasibility.

Untangling the interplay of dissolved organic matters variation with microbial symbiotic network in sludge anaerobic fermentation triggered by various pretreatments

Various pretreatments are commonly adopted to facilitate dissolved organic matter (DOM) release from waste activated sludge (WAS) for high-valued volatile fatty acids (VFAs) promotion, while the interplay impact of DOM dynamics transformation on microbial population and metabolic function traits is poorly understood. This work constructed “DOM-microorganisms-metabolism-VFAs” symbiotic ecologic networks to disclose how DOM dynamics variation intricately interacts with bacterial community networks, assembly processes, and microbial traits during WAS fermentation. The distribution of DOM was altered by different pretreatments, triggering the release of easily biodegradable compounds (O/C ratio > 0.3) and protein-like substance. This alteration greatly improved the substrates biodegradability (higher biological index) and upregulated microbial metabolism capacity (e.g., hydrolysis and fatty acid synthesis). In turn, microbial activity modifications augment substance metabolism level and expedite the conversion of highly reactive compounds (proteins-like DOM) to VFAs, leading to 1.6–4.2 fold rise in VFAs generation. Strong correlations were found between proteins-like DOM and topological properties of DOM-bacteria associations, suggesting that high DOM availability leads to more intricate ecological networks. A change in the way communities assemble, shifting from stronger uniform selection in pH10 and USp reactors to increased randomness in heat reactor, was linked to DOM composition alterations. The ecologic networks further revealed metabolic synergy between hydrolytic-acidogenic bacteria (e.g., Bacteroidota and Firmicutes) and biodegradable DOM (e.g., proteins and amino sugars) leading to higher VFAs generation. This study provides a deeper knowledge of the inherent connections between DOM and microbial traits for efficient VFAs biosynthesis during WAS anaerobic fermentation, offering valuable insights for effective WAS pretreatment strategies.

Deep insights into the roles and microbial ecological mechanisms behind waste activated sludge digestion triggered by persulfate oxidation activated through multiple modes

Persulfate oxidation (PS) is widely employed as a promising alternative for waste activated sludge pretreatment due to the capability of generating free radicals. The product differences and microbiological mechanisms by which PS activation triggers WAS digestion through multiple modes need to be further investigated. This study comprehensively investigated the effects of persulfate oxidation activated through multiple modes, i.e., ferrous, zero-valent iron (ZVI), ultraviolet (UV) and heat, on the performance of sludge digestion. Results showed that PS_ZVI significantly accelerated the methane production rate to 12.02 mL/g VSS. By contrast, PS_Heat promoted the sludge acidification and gained the maximum short-chain fatty acids (SCFAs) yield (277.11 ± 7.81 mg COD/g VSS), which was 3.41-fold compared to that in PS_ZVI. Moreover, ferrous and ZVI activated PS achieved the oriented conversion of acetate, the proportions of which took 73% and 78%, respectively. MiSeq sequencing results revealed that PS_Heat and PS_UV evidently enriched anaerobic fermentation bacteria (AFB) (i.e., Macellibacteroides and Clostridium XlVa). However, PS_Ferrous and PS_ZVI facilitated the enrichment of Woesearchaeota and methanogens. Furthermore, molecular ecological network and mantel test revealed the intrinsic interactions among the multiple functional microbes and environmental variables. The homo-acetogens and sulfate-reducing bacterial had potential cooperative and symbiotic relationships with AFB, while the nitrate-reducing bacteria displayed distinguishing ecological niches. Suitable activation modes for PS pretreatments resulted in an upregulation of genes expression responsible for digestion. This study established a scientific foundation for the application of sulfate radical-based oxidation on energy or high value-added chemicals recovery from waste residues.

Synergistic effects and mechanisms of plasma coupled with peracetic acid in enhancing short-chain fatty acid production from sludge: Motivation of reactive species and metabolic tuning of microbial communities

Suitable waste activated sludge (WAS) pretreatments that boost short-chain fatty acid (SCFA) production from anaerobic fermentation are essential for carbon emission reduction and sludge resource utilization. This study established an efficient WAS pretreatment process combining atmospheric pressure plasma jet (APPJ) with peracetic acid (PAA). The maximum SCFA production (6.5-fold that of the control) largely increased under the optimal conditions (PAA dosage = 25 mg/g VSS (volatile suspended solids), energy consumption = 20.9 kWh/m3). APPJ/PAA pretreatment enhanced the production of multiple reactive species (including OH, CH3C(O)O, 1O2, ONOO–, O2–, and eaq−) and strengthened the effects of H2O2, heat, and light. This synergistically solubilized WAS and released organic substrates for SCFA-producing microbes. In addition, the enrichment of SCFA-producing bacteria and the decrease in SCFA-consuming bacteria favored SCFA accumulation. The key genes encoding for the main substrate metabolism and SCFA production in the metabolic pathway of fermentation were also enhanced.

Heat-enhanced sulfite pretreatment improves the release of soluble substances and the stimulation of methanogenic pathways for anaerobic digestion of waste activated sludge

Waste activated sludge pretreatment is effective in improving sludge hydrolysis rate and methane production. Our previous study revealed that sulfite could be a viable method for sludge pretreatment. To further improve methane production, this study employed an integrated strategy by combining sulfite and heat pretreatment. WAS from a local full-scale plant was pretreated with heat-enhanced sulfite pretreatment (HESP) at 25, 35, 55 °C. Compared with the control (no sulfite, 25 °C), soluble substances (e.g., chemical oxygen demand, protein, polysaccharides, nitrogen and phosphorus) could be significantly enhanced by the absence of sulfite and the increasing temperature. A variation of − 8.32–19.90% in cumulative methane production was observed. Moreover, methane production could be significantly enhanced by 14.15% at sulfite of 300 mg S/L and temperature of 35 °C, while kinetic analysis showed that the highest methane production potential (1.43 times of the control) was obtained at this level. Besides, the microbial structure and pathways reveal that HESP promotes the enrichment of methanogenic bacteria and facilitates methanogenic metabolism. The findings of this study suggest that the HESP could be promising in enhancing methane production, particularly considering the reuse of sulfite-laden industrial wastes and the heat as the by-products of the anaerobic digestion plant with biogas power generation, but certain experimental conditions should be verified case by case.

Process configuration of combined ozonolysis and anaerobic digestion for wastewater treatment

Abstract Industrial activities and increased human population have made wastewater streams not entirely amenable to conventional treatment methods. Anaerobic digestion (AD) can treat such wastewaters with the advantage of bioresource recovery. However, the presence of solids and recalcitrant compounds in most wastewater streams may affect the AD process. Thus, combining AD with advanced oxidation processes (AOPs) such as ozonolysis is necessary. Ozonolysis can improve the biodegradability of wastewater substrates or eliminate biorecalcitrant pollutants that escape the AD process. This study combined ozonolysis with AD to treat waste activated sludge (WAS) and distillery wastewater (DWW). When applied as a pre-treatment, ozonolysis caused the rigid cell walls in WAS to rupture and solubilised the extracellular polymeric substances (EPS), leading to increased biodegradability. For the DWW, ozonolysis pre-treatment reduced the biorecalcitrant aromatic compounds to simple aliphatic compounds, thereby increasing biodegradability. In the ensuing anaerobic process, the WAS pre-treatment improved TSS and COD reductions and a 230% increase in cumulative biogas production. For the DWW, the ozonolysis pre-treatment did not significantly impact COD reduction or biogas production; however, ozonolysis as a post-treatment removed the color causing biorecalcitrant melanoidins from the anaerobically digested effluent and solubilised the sludge (TSS) washed out from the AD unit. Therefore, the AD-ozonolysis process configuration depends on the substrate being treated. Ozonolysis is best applied pre-AD for WAS treatment and post-AD for DWW.

Low-temperature thermal pre-treated sewage sludge for feeding of black soldier fly (Hermetia illucens) larvae: Protein, lipid and biodiesel profile and characterization

Previous work showed that low-temperature thermal pre-treatment of waste activated sludge (WAS) under different temperatures (30, 60, 75, 90 °C) and durations (2, 4, 8, 16 h) prior to black soldier fly larvae (BSFL) rearing could improve the larval growth. In this work, the biochemical profiles of WAS-fed BSFL and the characteristics of biodiesel produced were reported. The BSFL fed with pre-treated WAS had high protein contents (44%–54%) and moderate lipid contents (21%–25%). The WAS pre-treated at 90 °C for 16 h produced BSFL with the highest protein and lipid yields, achieving 69% and 71% of increments, respectively, as compared with the controlled WAS. Subsequently, high conversion of lipid into biodiesel (>90%) could be achieved through the acid-catalyzed transesterification process. The BSFL biodiesel was dominated by saturated fatty acid methyl esters (FAME), with C12:0 being the abundance. This unique FAME profile enabled BSFL biodiesel to have low iodine value, high cetane number and more oxidatively stable as compared with other reported biodiesels like palm oil and rapeseed oil biodiesels. The BSFL biodiesel also satiated the biodiesel standards of EN 14214 and ASTM D6751, except for the flash point, which was still higher and safer than petroleum diesel. In short, the thermal pre-treatment of WAS was effective in promoting BSFL growth and its lipid yield, ultimately leading to higher biodiesel production.

Sulfite pretreatment enhances the medium-chain fatty acids production from waste activated sludge anaerobic fermentation

Production of high-value medium chain fatty acids (MCFAs) from anaerobic fermentation of waste activated sludge (WAS) has been considered as a promising alternative for renewable energy resources. However, the low biodegradability of WAS greatly limits the anaerobic fermentation performance. This study proposed and demonstrated a novel approach, sulfite pretreatment, to efficiently produce MCFAs through anaerobic fermentation of WAS. Pretreatment of WAS at a sulfite concentration of 100–500 mg S/L for 24 h effectively improved the MCFAs production and MCFAs selectivity and the promotion effect was positively correlated with the sulfite concentration used in pretreatment (Pearson's R > 0.9). The maximum MCFAs production of 6.84 g COD/L and MCFAs selectivity of 39.1 % were both achieved under 500 mg S/L sulfite pretreatment, which accounts for 2.6 times and 2.4 times of the control, respectively (MCFAs production of 2.62 g COD/L and MCFAs selectivity of 16.4 % in the control). Sulfite pretreatment also enhanced the WAS degradation from 25 ± 2 % in the control to a maximum of 39 ± 2 % under 500 mg S/L sulfite pretreatment. The electron transfer efficiency and COD flows from the substrate to products were enhanced by up to 25 % due to the sulfite pretreatment, which supports the enhanced WAS degradation. Sulfite pretreatment also promoted the solubilization, hydrolysis, and acidification processes during the anaerobic fermentation by up to 200 %, 60 %, and 45 %, respectively, which subsequently makes more substrates available for MCFAs production. The findings from this study provide a potential solution of using industrial sulfite-laden wastes for WAS pretreatment, to enhance the MCFAs production at a minimized cost.

Microbial community structure and potential function associated with poly-3-hydroxybutyrate biopolymer-boosted activation of peroxymonosulfate for waste-activated sludge decontamination

Excess waste-activated sludge (WAS) is a major biosolid management problem due to its biohazardous and recalcitrant content of phthalate esters (PAEs). This study aimed to assess the combined use of biopolymer, poly-3-hydroxybutyrate and peroxymonosulfate to degrade PAEs and decontaminate WAS. Poly-3-hydroxybutyrate was biosynthesized by Cupriavidus sp. L7L. The combined poly-3-hydroxybutyrate and peroxymonosulfate process removed 86 % of PAEs from WAS in 12 h. The carbonyl groups of poly-3-hydroxybutyrate were conducive to peroxymonosulfate activation leading to PAE degradation followed the radical pathway and surface-mediated electron transfer. Poly-3-hydroxybutyrate and peroxymonosulfate also enriched the PAE-biodegrading microbes in WAS. The microbial population and the functional composition in response to peroxymonosultate treatment was identified, with the genus Sulfurisoma being the most abundant. This synergistic treatment, i.e., advanced oxidation process, was augmented by highly promising microbial polyesters, exhibited important implications for WAS pretreatment toward circular bioeconomy that encompasses carbon–neutral biorefinery and mitigate pollution.

Moderate potassium ferrate dosage enhances methane production from the anaerobic digestion of waste activated sludge

: The annual increase of waste activated sludge (WAS) has become an urgent problem to be solved in sewage plants worldwide. Anaerobic digestion (AD) of WAS is an attractive choice to maximize the resource utilization rate. Nevertheless, the disintegration of sludge complex polymers is difficult, resulting in low bioconversion rate. Potassium ferrate (PF), as a green oxidant with strong oxidizing property, has been attracted great attention in WAS pretreatment recently. The effects of PF pretreatment on WAS hydrolysis and its dosage-response on methane production were investigated in the present study. Results show that as PF dosage raise from 0 to 50 g-K2FeO4/ kg-TS (total solids), the methane yield enhanced significantly by 40.3% from 0.083 to 0.12 L/g-VSadded (volatile solids). Nevertheless, the further increase of PF dosage resulted in the decreased methane production. Especially with the PF dosage of 500 g-K2FeO4/ kg-TS, methane production even slightly lower than the control reactor without PF oxidation. The mechanism analysis showed that although the dissolution of polysaccharides and proteins were enhanced with the high dosage of PF, the accompanying released humic-like substances and high concentration of ferric ions should be the main reasons inhibiting methane production.

Distinct effects of typical sludge pretreatment approaches on the antibiotic resistance genes variations, associated bacterial community dynamics and metabolic activities during anaerobic fermentation process

Anaerobic fermentation is effective for waste activated sludge (WAS) disposal to realize resource generation and pollutants reduction, and various pretreatments were commonly applied to improve the performance. This work mainly investigated the effects of typical WAS pretreatment approaches on the antibiotic resistance genes (ARGs, as emerging contaminants) removal during anaerobic fermentation processes and unveiled the underlying mechanisms. The results indicated that all the pretreatment strategies exhibited evident effects on the overall ARGs removal with the order of Fe2+ activated persulfate (PS/Fe2+) > pH 10 > Ultrasonication > Heat, and showed selective removal tendency for the specific ARGs (namely easily removed (aadA1 and sul1) and persistent ARGs). Mechanistic analysis demonstrated that the pretreatments disrupted the extracellular polymeric substances (EPS) and rose the cell membrane permeability (particularly for PS/Fe2+ and Heat). Then the increased ARGs release benefitted the subsequent reduction of mobile genetic elements (MGEs) and extracellular ARGs (especially for PS/Fe2+ and pH10), resulting the ARGs attenuation. Pretreatments significantly shifted the microbial community structure and the abundances of potential ARGs hosts (i.e., Sulfuritalea, and Denitratisoma). Also, the different pretreatments exhibited distinct effects on the microbial metabolic traits related with ARGs proliferation (i.e., ABC transporters, two-component system and bacterial secretion systems), which also contributed to the ARGs attenuations during WAS fermentation. The partial least-squares path modeling (PLS-PM) analysis indicated that the bacterial community (total effects = 0.968) was key factor determining ARGs fates.

Urine pretreatment significantly promotes methane production in anaerobic waste activated sludge digestion

Methane production of waste activated sludge (WAS) in anaerobic digestion is hindered due to the rate-limited hydrolysis process and the low methane potential of WAS. Pretreatment of WAS is a common and appealing strategy to improve methane production in anaerobic digestion. In this study, we proposed to use urine, an easily obtained human waste with high ammonium concentration and pH, as a novel pretreatment strategy for anaerobic WAS digestion. Urine pretreatment at levels of 5–30 % (Vurine/Vurine+WAS) could substantially enhance methane production by 5–35 % in biochemical methane potential (BMP) tests, with the highest methane production of 179.6 ± 3.3 mL/g volatile solids (VS) achieved under the highest level of urine (i.e. 30 % urine addition). Based on the model analysis, the biochemical methane potential (B0) and hydrolysis rate of WAS (k) rose from 131.9 mL/g VS and 0.19 d−1 in the control without pretreatment to 136.3–178.2 mL/g VS and 0.22–0.30 d−1, respectively, after the urine pretreatment (5–30 % addition). Urine pretreatment with 5–30 % addition also improved the degradation extent (Y) of WAS by 3–35 %. The promising results indicate that urine pretreatment in anaerobic digestion is a promising technology to improve the efficiency of anaerobic digestion with environmental and economic benefits.

Impact of divalent cations on lysozyme-induced solubilisation of waste-activated sludge: Perspectives of extracellular polymeric substances and surface electronegativity

Lysozyme hydrolysis can accelerate waste-activated sludge (WAS) solubilisation, which can significantly shorten the process and promote the efficiency of anaerobic digestion. This study investigated the impact of divalent cations on lysozyme-induced solubilisation of WAS. The performance of lysozyme pretreatment was dramatically inhibited by Mg2+ and Ca2+. Compared to the control group, the amount of net SCOD, protein, and polysaccharides released to the supernatant were reduced by 36.6%, 44.7%, and 35.8%, respectively, in the presence of divalent cations. The extracellular polymeric substance (EPS) matrix became tightly bound, resulting in fewer proteins and polysaccharides being extracted from loosely-bound EPS (LB-EPS) with divalent cations, which was detrimental to the solubilisation of WAS. Divalent cations decreased the surface electronegativity of sludge particles and prolonged the adsorption of lysozymes by sludge flocs. More than 16.6% of total lysozymes remained in the liquid phase of WAS after 240min Mg2+ and Ca2+ strengthened the binding among proteins and polysaccharides and promoted the intermolecular cross-linking of polysaccharides. The EPS matrix formed a dense spatial reticular structure that blocked the transfer of lysozymes from the EPS matrix to the pellet. As a result, the lysozymes accumulated in LB-EPS rather than hydrolysing the microorganism's cell wall. This study provides a new perspective on the restriction of WAS pretreatment with lysozymes and optimises the method of lysozyme-induced solubilisation of WAS.

Removal of 4-nonylphenol in activated sludge by peroxymonosulfate activated with sorghum distillery residue-derived biochar

The presence of 4-nonylphenol (4-NP), an endocrine disrupting chemical, waste activated sludge (WAS) or biosolids at elevated content requires effective method for 4-NP reduction in total sludge management. Herein, sorghum distillery residue-based biochar-activated peroxymonosulfate (SDRBC/PMS) system was studied as pretreatment of WAS. Results indicated 91% of 4-NP removal at pH 6.0 in the presence of 3.1 × 10−6 M and 0.8 g L−1 PMS and SDRBC500, individually. The synergetic effects of singlet oxygen (1O2) and the abundant functional sites (C = O/C–O content) of SDRBC significantly improved 4-NP degradation. The decreased fluorescent dissolved organic matter (DOM) in the sludge also enhanced the pretreatment efficiency. Moreover, the enrichment of the Nitrospira functional bacteria in the microbial community yielded the highest 4-NP degradation in the SDRBC/PMS-pretreated sludge. The SDRBC/PMS system functions mainly via nonradical-mediated oxidation pathway in pretreating WAS in particular and potentially by combined advanced oxidation and biodegradation processes for wastewater treatment in general.

Production of volatile fatty acids concomitant with phosphorus removal and lignin recovery by co-fermentation of waste activated sludge and black liquor

Waste activated sludge (WAS) and black liquor (BL) are the stubborn solid waste and wastewater in the industry that need high investment and operational costs for treatment. In this study, co-fermentation of WAS and BL was performed following a novel process for the production of volatile fatty acids (VFAs) concomitant with phosphorus removal and lignin recovery. BL offers alkaline liquor for WAS pretreatment, and the organic carbon in BL can be used for fermentation. The results showed that the semi-continuous fermentation test at pH 10 and the addition of 800 mg/L of Mg2+ were the optimal conditions for the production of VFAs (approximately 15,000 mg/L) and P removal (≈94%). Additionally, Mg2+ was suited to remove P due to the weak adsorption of Mg2+ by BL under alkaline conditions. Moreover, the composition of VFAs was affected by the pH, for example, high ratios of acetate and propionate were obtained under conditions of high and low pH, respectively. The dominant functional bacteria of Alkalibacterium, Propionibacterium, Proteiniphilum, and Tessaracoccus were found through the analysis of microbial diversity to be responsible for the production of VFAs. The bioconversion of small molecular lignin was also demonstrated through the characterization analyses. Co-fermentation was suggested as an economic and eco-friendly strategy for the treatment and resource utilization of WAS and BL via the overall assessment of the technical process.

Elucidating the production and inhibition of melanoidins products on anaerobic digestion after thermal-alkaline pretreatment

The refractory organics released from waste activated sludge (WAS) are unwanted produced in thermal-alkaline pretreatment, which are not well documented. In this study, we refer to them as melanoidins products (MPs) with characteristics of high molecular weight and inhibition to microbes. The results showed that these MPs from thermal-alkaline (80 °C and pH 10) pretreatment of WAS were identified with a broad molecular weight (>1000 Da). Dark-colored MPs were further verified from glucose and tryptophan as the model components, with values of UV280 and UV420 increasing. The produced MPs with a molecular weight of 1220, 6835, and even 21,200,000 Da were confirmed by SEC-HPLC. Unexpectedly, MPs were found to be electroactive with higher redox peak values than that of humic acids, which were almost not degraded by anaerobes as revealed by SEC-HPLC and 3D-EEM spectra. For the first time, the results demonstrated that MPs delayed volatile fatty acids production and reduced the methane yield (22–26% lower), which was likely attributed to the toxicity and/or electrons competition with anaerobes such as Methanosaeta. Thus, it is clear that MPs negatively impact anaerobic digestion after thermal-alkaline pretreatment, which shall be re-evaluated to minimize MPs when producing biochemicals from WAS.

Improved energy balance at a municipal wastewater treatment plant through waste activated sludge low-temperature alkaline pretreatment

Sludge management has a significant impact on operating costs in municipal wastewater treatment plants (WWTPs). The current trend is to optimize the sludge management in order to enhance the energy independence from external energy suppliers, while reducing the operating costs of the WWTP. One of the methods is through the pretreatment of waste activated sludge (WAS). In this work, low-temperature alkaline pretreatment of WAS was examined as a method of improving the economic balance of the WWTP. In the initial pretreatment tests, the impacts of NaOH dose, temperature and reaction time on COD release as well as the degree of sludge disintegration were examined. Semi-continuous anaerobic digestion (AD) trials were then performed for pretreated WAS in selected conditions with low NaOH dosage for which no pH adjustment was required (16 g of NaOH/kgTS of WAS, 60 °C, 60 min). The tests showed an increase in methane yield from 210.4 ± 10.9 mL CH4/gVS to 248.8 ± 13.1 mL CH4/gVS and 267.1 ± 14.3 mL CH4/gVS for HRT 15 d and HRT 21.5 d, respectively. Energy balance and economic calculations for a full-scale WWTP were conducted based on the obtained results. It was concluded that it would be possible to increase electricity production from methane originated from AD of pretreated WAS up to 27% as well as to reduce the amount of dewatered sludge up to 8.7%. Energy balance and cost-benefit analyses indicated a possibility to reduce the operating cost by over 300,000 EUR/year in the case of a 1,200,000 people-equivalent WWTP.