Sludge Stabilization Research Articles

Mutualistic symbiosis of fungi and nitrogen-fixing bacteria in halophilic aerobic granular sludge treating nitrogen-deficient hypersaline organic wastewater

Hypersaline organic wastewater is characterized as being nitrogen-deficient, and is easily prone to sludge bulking. In this study, the stability of halophilic aerobic granular sludge (HAGS) for the treatment of hypersaline organic wastewater is explored. Along with the decrease of influent ammonium, the bacterial population substantially reduced, whereas the fungal population continuously increased in HAGS. Saccharomycetales in fungi become the dominant sequence (99.78%) in HAGS bulking. Additionally, Halanaerobium (77.47%) remained prevalent in HAGS despite bacterial washout. Halanaerobium, a nitrogen-fixing genus of bacteria, provided nitrogen for ammonium-assimilating fungi. Saccharomycetales encapsulating HAGS reduced the transfer efficiency of dissolved oxygen, thereby creating favorable growth conditions for Halanaerobium. This paper for the first time highlights the mutualistic symbiosis of fungi and bacteria in HAGS treating the hypersaline organic wastewater. The study lays the foundation for the control and recovery of HAGS bulking.

Development of a Hybrid Technological Scheme for the Treatment of Anaerobically Fermented Sludge (Digestat) of Wastewater of the Food Industry

The issue of dewatering and disposal of sewage sludge is one of the most urgent due to the acute shortage of land resources, the negative ecological burden on water resources, soils and the atmosphere of these sludges in case of their accumulation without proper treatment. Anaerobic stabilization of food production wastewater sludge is one of the most widespread methods of processing this type of sludge due to the possibility of obtaining an important energy resource – biogas. The sludge obtained after anaerobic stabilization in methane tanks is called digestate, and it also needs treatment and further disposal. Digestate can be used as a fertilizer if sanitary and hygienic requirements are met. The development of a technological scheme for processing wastewater digestate is a complex issue that does not have one correct solution. A hybrid technological process for processing wastewater digestate of the food industry is proposed on the basis of experimental studies. Experimental studies include dewatering anaerobically stabilized sludge on a multi-disc dehydrator using dilution of the sludge itself due to its significant viscosity, addition of coagulant and flocculant. Cake with a moisture content of about 65–80% can be transported and used as fertilizer for agriculture. The separated filtrate from the digestate according to the technological scheme is proposed to be purified on two stages of membranes. The efficiency of cleaning the liquid fraction of the digestate on a two-stage membrane installation according to two variants showed the following results: variant 1 (VSEP + RO) – 95%, variant 2 (ZI + RO1 + RO2) – 94%. The VSEP system uses a hermetic RO membrane, so a two-pass membrane process (VSEP+RO) is suitable to achieve the end goal (permeate obtained can be reused), while a ZI membrane requires a three-pass membrane process to achieve the same goal. The achieved parameters make it possible to use the obtained permeate for the production needs of the enterprise or in the technological scheme of the digestate processing itself for dilution of the sediment or for the preparation of reagent solutions. The resulting products (cake and concentrates after membranes) can be used as fertilizers.

Effect of in situ ultrasonic wave and influent ammonia nitrogen fluctuation on stability of aerobic granular sludge

ABSTRACT This study elucidates the impact of fluctuating influent conditions and in situ ultrasonic wave exposure on the stability of aerobic granular sludge (AGS) in the treatment of simulated wastewater emanating from rare earth mining operations. During a stable influent period spanning from Day 1 to Day 95, the seed granules underwent an initial disintegration followed by a re-granulation phase. The secondary granulation was achieved on Day 80 and Day 40 for the ultrasonic reactor (R1) and the control reactor (R2), respectively. Notably, granules formed in R1 exhibited a more porous structure compared to those generated in R2. Subsequently, when the ammonia nitrogen in the influent oscillated between 100 and 500 mg/L during Days 96-140, both reactors yielded compact and densely structured granules. Nitrogen removal profiles were comparable between the two reactors: the removal efficiencies for ammonia nitrogen and total inorganic nitrogen escalated from 95% and 80%, respectively, during Days 1-95, to 95% and 90%, respectively, post-Day 140. A suite of performance metrics indicated that steady-state granules from R1 outperformed those from R2 across several parameters. Specifically, the nitrification/denitrification rates, and relative abundance of denitrifying bacteria were all higher in granules from R1. Conversely, the relative abundance of nitrifying bacteria was comparable between granules from both reactors. However, R1 granules demonstrated lower sludge concentration and smaller average particle size than their R2 counterparts. In conclusion, the AGS system demonstrated robust resilience to fluctuating ammonia nitrogen, and the application of ultrasonic waves significantly enhanced granular activity while achieving in situ sludge reduction.

Rapid static feeding combined with Fe2+ addition for improving the formation and stability of aerobic granular sludge in low-strength wastewater

Aerobic granular sludge (AGS) needs a long start-up time and always shows unstable performance when it is used to treat low-strength wastewater. In this study, a rapid static feeding combined with Fe2+ addition as a novel strategy was employed to improve the formation and stability of AGS in treating low-strength wastewater. Fe-AGS was formed within only 7 days and showed favorable pollutant removal capability and settling performance. The ammonia nitrogen (NH4+-N) and chemical oxygen demand (COD) concentration in the effluent were lower than 5 mg/L and 50 mg/L after day 23, respectively. The sludge volume index (SVI) and mixed liquid suspended solids (MLSS) was 37 mL/g and 2.15 g/L on day 50, respectively. Rapid static feeding can accelerate granules formation by promoting the growth of heterotrophic bacteria, but the granules are unstable due to filamentous bacteria overgrowth. Fe2+ addition can inhibit the growth of filamentous bacteria and promote the aggregation of functional bacteria (eg. Nitrosomonas, Nitrolancea, Paracoccus, Diaphorobacter) by enhancing the secretion of extracellular polymeric substances (EPS). This study provides a new way for AGS application in low-strength wastewater treatment.

Recent advances in the structure and function of microbial community in anaerobic granular sludge

Anaerobic granular sludge (AnGS), a self-immobilized aggregate containing various functional microorganisms, is considered as a promising green process for wastewater treatment. AnGS has the advantages of high volume loading rate, simple process and low excess sludge generation, thus shows great technological and economical potentials. This review systematically summarizes the recent advances of the microbial community structure and function of anaerobic granular sludge, and discusses the factors affecting the formation and stability of anaerobic granular sludge from the perspective of microbiology. Moreover, future research directions of AnGS are prospected. This review is expected to facilitate the research and engineering application of AnGS.

Revealing the intrinsic mechanisms for accelerating nitrogen removal efficiency in the Anammox reactor by adding Fe(II) at low temperature

Fe(II) is an essential trace element for anaerobic ammonium oxidation bacteria (AAOB) metabolism, and can improve the nitrogen removal efficiency of anaerobic ammonia oxidation (Anammox). Here we operated two identical expanded granular sludge bed (EGSB) reactors at low temperature (15 ± 3 °C) for 154 days. Reactor 1 (R1) received additional Fe(II) (0.12 mmol/L) during the late startup phase, while reactor 0 (R0) served as the control and did not receive extra Fe(II). Nitrogen removal in R1 became stable at 55 d of operation, ten days earlier than R0. The nitrogen removal rate (NRR) of R1 was 1.64 kg N m−3 d−1 and its TN removal rate was as high as 89%, while R0 only reached 75%. The addition of Fe(II) was further beneficial to aggregation and stability of the granular sludge, and the used sludge of both reactors showed enrichment for AAOB populations compared to the inoculum, for instance, increased abundance of Candidatus-Kuenenia and in particular of Candidatus-Brocadia (from 0.17% to 10.10% in R0 and 7.79% in R1). Diverse microbial species and complex microbial network structure in R1 compared to R0 promoted the coupled denitrogenation by Anammox, dissimilatory nitrate reduction to ammonium (DNRA), nitrate-dependent Fe oxidation (NDFO), and ferric ammonium oxidation (Feammox). In addition, the microbial community in R1 was more resistant to short-term low temperature (2–7 °C) starvation, illustrating a further positive effect of adding Fe(II) during the startup phase of an Anammox reactor.

Algal-bacterial granular sludge for simultaneous denitrification and yttrium removal

This study investigated the performance and stability of algal-bacterial granular sludge (ABGS) for the treatment of inorganic wastewater containing ammonia and Y(III), which aimed to shed light on efficient treatment of yttrium-rich rare earth mine wastewater. By seeding heterotrophic granules and dosing exogenous algae, cationic polyacrylamide and sodium acetate in a photo-sequencing batch reactor, the algal and granular symbiosis system was successfully established on Day 50, and mature ABGS was harvested on Day 165. When the concentration of Y(III) was no more than 4 mg/L, the system showed good performance for simultaneous removal of nitrogen and Y(III). However, further increasing the Y(III) concentration to 30 mg/L in Days 144–210 gradually inhibited the bacterial activity and killed most of the functional algae, resulting in significant decrease of the activity of bacteria and chlorophyll a content after Days 135 and 180, as well as the oxygen yield rate of the algae and ammonia oxidation rate after Days 140 and 95. The removal efficiency of total inorganic nitrogen maintained mostly above 90% in Days 46–153, and gradually decreased to approximately 50% in Days 154–210. The Y(III) removal efficiency remained above 98% in Days 96–125, and gradually decreased to approximately 60% in Days 126–210. Most of the algal genera disappeared on Day 210. Conversely, the increase of the relative abundance of Nitrosomonas and Thauera was observed. The nitrogen removal pathways included denitrification and algal assimilation. However, the contribution rate of algae gradually decreased from 22% to 4% due to the accumulation of Y.

Enhancing methane production from anaerobic digestion of secondary sludge through lignosulfonate addition: Feasibility, mechanisms, and implications

This study explores the feasibility of using lignosulfonate, a byproduct of the pulp and paper industry, to facilitate sludge anaerobic digestion. Biochemical methane potential assays revealed that the maximum methane production was achieved at 60 mg/g volatile solids (VS) lignosulfonate, 22.18 % higher than the control. One substrate model demonstrated that 60 mg/g VS lignosulfonate boosted the hydrolysis rate, biochemical methane potential, and degradation extent of secondary sludge by 19.12 %, 21.87 %, and 21.11 %, respectively, compared to the control. Mechanisms unveiled that lignosulfonate destroyed sludge stability, promoted organic matter release, and enhanced subsequent hydrolysis, acidification, and methanogenesis by up to 31.30 %, 74.42 % and 28.16 %, respectively. Phytotoxicity assays confirmed that lignosulfonate promoted seed germination and root development of lettuce and Chinese cabbage, with seed germination index reaching 170 ± 10 % and 220 ± 22 %, respectively. The findings suggest that lignosulfonate addition offers a sustainable approach to sludge treatment, guiding effective management practices.

Molecular transformation pathway and bioavailability of organic phosphorus in sewage sludge under vermicomposting

Phosphorus reclamation from sewage sludge is essential for sustainable phosphorus management, as large quantities of phosphorus afflux into wastewater treatment plants and are finally enriched in sewage sludge via phosphorus removal technologies. Meanwhile, vermicomposting is a cost-effective biotechnique for sludge stabilization. This work unveiled the molecular transformation pathway and bioavailability of organic phosphorus (OP) in sludge under vermicomposting with solution 31P NMR, FT-ICR MS and enzymatic hydrolysis assay. In conclusion, vermicomposting transformed OP in two stages. In stage I (day 0 to 14), macromolecule CHONP such as phospholipids, phosphoproteins and nucleic acid were decomposed into orthophosphate and high bioavailability OP including flavin mononucleotide, flavin mononucleotide hydrate and N6-isopentenyladenosine 5′-monophosphate under the action of earthworm intestinal flora. This resulted in the bioavailability of OP reaching a maximum of 13.58 mg/L on day 14. In stage II (day 14 to 28), the enzyme in vermicompost began to dominate the transformation of OP. Under the catalysis of phosphate, high bioavailability orthophosphate monoester was decomposed into orthophosphate. Nitrogen-containing aromatic OP polymerization produced humic acid-like OP under the catalysis of ligase. And phytic acid-like OP were produced under the catalysis of transferase. These led to the OP bioavailability decreasing to 5.60 mg/L on day 28. This work provides a new perspective on sludge phosphorus recovery and use.

Effect of lysozyme combined with hydrothermal pretreatment on excess sludge and anaerobic digestion

Anaerobic digestion (AD) is widely employed for sludge stabilization and waste reduction. However, the slow hydrolysis process hinders methane production and leads to prolonged sludge issues. In this study, an efficient and eco-friendly lysozyme pre-treatment method was utilized to address these challenges. By optimizing lysozyme dosage, hydrolysis and cell lysis were maximized. Furthermore, lysozyme combined with hydrothermal pretreatment enhanced overall efficiency. Results indicate that: (1) When lysozyme dosage reached 90 mg/g TS after 240 min of pretreatment, SCOD, soluble polysaccharides, and protein content reached their maxima at 855.00, 44.09, and 204.86 mg/L, respectively. This represented an increase of 85.87%, 365.58%, and 259.21% compared to the untreated sludge. Three-dimensional fluorescence spectroscopy revealed the highest fluorescence intensity in the IV region (soluble microbial product), promoting microbial metabolic activity. (2) Lysozyme combined with hydrothermal pretreatment significantly increased SCOD, soluble proteins, and polysaccharide release from sludge, reducing SCOD release time. Orthogonal experiments identified Group 3 as the most effective for SCOD and soluble polysaccharide release, while Group 9 released the most soluble proteins. The significance order of factors influencing SCOD, soluble proteins, and polysaccharide release is hydrothermal temperature > hydrothermal time > enzymatic digestion time.(3) The lysozyme-assisted hydrothermal pretreatment group exhibited the fastest release and the highest SCOD concentration of 8,135.00 mg/L during anaerobic digestion. Maximum SCOD consumption and cumulative gas production increased by 95.89% and 130.58%, respectively, compared to the control group, allowing gas production to conclude 3 days earlier.

Conversion of recycled sludge waste into high value-added ceramics as engineering construction materials: Fabrication, characterization and performance evaluation

Sludge from municipal wastewater treatment plants usually exhibits extremely homologous traits with clay in both mineralogical component and chemical composition, and accordingly it can be utilized as an alternative feedstock for clay to fabricate engineering construction materials and advance sludge valorization. In this work, different proportions of wastewater treatment plant sludge (WTPS) were incorporated into kaolin to develop value-added construction ceramic materials. The thermal behavior, crystalline composition, physicochemical performance, microscopic characteristics and sintering mechanism of value-added ceramics were investigated. The results showed that WTPS not only contained a large amount of inorganic components such as SiO2, Al2O3 and Fe2O3, but also rich organic compounds, which contributed to the formation of pore structure inside the ceramics during sintering. Different WTPS addition did not affect the types of crystalline components in sintered ceramics, but markedly impacted the sintering behavior. Only when the WTPS dosage reached 40 wt%, the original mixtures would be fully sintered into construction ceramics with the apparent porosity of 11.30 %, thermal conductivity of 0.50 W/(m·K), bulk density of 2.22 g/cm3, linear shrinkage and volume shrinkage of 14.95 % and 38.86 % respectively, as well as vastly low water absorption (0.58 %) and excellent flexural strength (84 MPa). However, with the WTPS content up to 50 wt%, the flexural strength of sintered ceramics was reduced to 50 MPa, despite the elevated sintering degree, which was related to the high formation of liquid phase and the violent expansion of several closed pores. Therefore, converting WTPS into high value-added construction ceramic products is an operable and beneficial way to achieve sludge waste recycling, reduction and stability.

Enhancing methane production and organic loading capacity from high solid-content wastewater in modified granular activated carbon (GAC)-amended up-flow anaerobic sludge blanket (UASB)

Anaerobic digestion of high solid-content wastewater is hindered by high organic loading rates (OLRs). Granular activated carbon (GAC) was reported to promote direct interspecies electron transfer (DIET) and enhance reactor performance. In this study, three up-flow anaerobic sludge blanket (UASB) reactors were supplied with GAC in different locations: bottom (R1), top (R2), and bottom+top (R3). The performances of three reactors at different OLRs treating high solid-content wastewater were evaluated. At a low OLR, the highest methane yield (74 ± 4 %, g CH4-COD/g TCOD) was detected when GAC was supplied at top of the UASB (R2). When a high OLR was applied, the UASB supplemented with GAC at both bottom and top (R3) achieved the highest methane yield (66 ± 2 %, g CH4-COD/g TCOD), whereas the UASB supplemented with GAC at the top (R2) failed. Further studies on spatial distributions of sludge stability, specific methanogenic activities (SMAs), and microbial communities demonstrated the different impacts of GAC location on reactor performance and sludge characteristics under different OLRs. This study highlights the significance of considering organic loading capacity treating high solid-content wastewater when choosing GAC-based UASB systems.

Feasibility of ammonium sulfate recovery from wastewater sludges: Hydrothermal liquefaction pathway vs. anaerobic digestion pathway

This study evaluated two pathways to recover the nitrogen-content of wastewater sludges as ammonium sulfate (AmS) for use as fertilizer. The first pathway entails sludge stabilization by hydrothermal liquefaction (HTL) followed by recovery of AmS from the resulting aqueous product by gas permeable membrane (GPM) separation. The second one entails stabilization of the sludges by anaerobic digestion (AD) followed by recovery of AmS from the resulting centrate by GPM separation. A bench-scale GPM reactor is shown to be capable of recovering >90% of N in the feed. Recoveries of NH3–N in the HTL-pathway ranged 96–100% in 5.5–7.5 h at mass removal rates of 0.2–0.3 g N/day, yielding 3.3–6.0 g AmS/L of feed. Recoveries of 98% were noted in the AD-pathway in 4 h at mass removal rates of 0.06–0.97 g N/day and a yield of 1.7–2.1 g AmS/L of feed. Inductively coupled plasma optical emission spectrometer analysis confirmed that both pathways yielded AmS meeting the US EPA and European region guidelines for land application. The GPM reactor enabled higher nitrogen-recoveries in the HTL-pathway than those reported for current practice of AD followed by ammonia stripping, ion exchange, reverse osmosis, and/or struvite precipitation (96–100% vs. 50–90%). A process model for the GPM reactor is validated using performance data on three different feedstocks.

Experimental study on the strength and water stability of concentrated solution sludge solidified with sulfoaluminate cement combined with MSWI bottom ash

Concentrated solution sludge (CSS) produced by the submersion combustion technology conducted on the municipal solid waste (MSW) sanitary landfill leachate has special characteristics, such as high water content, low organic matter and heavy metal content and extremely high salt content. In the present work, sulphoaluminate cement (SAC) was used as main curing agent and municipal solid waste incineration (MSWI) bottom ash was collaborated as auxiliary curing agent to solidify the CSS. A series of unconfined compression tests, water stability test and microscopic observation tests were conducted on the solidified CSS samples with various curing agent combinations to quantitatively investigate the influence of different curing agents on the solidification effect of the CSS, and to interpret the physical mechanism of strength improvement and deterioration of the solidified CSS in curing and soaking stage. Research results indicate that: the 7 d unconfined compression strength (UCS) of the CSS solidified with 10% SAC is 168.6 kPa, 162.8 kPa and 158.8 kPa when the water cement ratio is 0.25, 0.30 and 0.35, respectively, which are larger than 50 kPa and can satisfy the strength requirement of landfill. The UCS of the CSS solidified with 50% SAC after soaking in water for 28 days is 329.4 kPa, 276.5 kPa and 202.0 kPa when the water cement ratio is 0.25, 0.30 and 0.35, respectively, and can satisfy the strength requirement of landfill concerning water stability of the solidified CSS; the 28d UCS of the CSS solidified with 40% SAC and an addition of 0%, 5%, 10% and 15% bottom ash is 1483.8 kPa, 2144.4 kPa, 2431.2 kPa and 1537.0 kPa, respectively, and decreased to 0 kPa, 52.9 kPa, 103.9 kPa and 51.0 kPa after soaking in water for 28 days; a reasonable bottom ash content is capable of improving the USC of the cement solidified CSS and there is an optimal dosage of bottom ash for enhancing the 28 d UCS of the cement solidified CSS, which is 5% for SAC content lower than 40% and 10% for SAC content higher than 40%. The improvement effect of the solidified CSS can be achieved by using 10% bottom ash as replacement for 10% SAC. The SEM and XRD test results indicate that: the formation of the spatial interlocking structure composed of the C-S-H gels and ettringite crystals generated by the interaction between SAC and bottom ash in soaking stage is the key factor for improving the water stability of the cement solidified CSS by adding a certain dosage of bottom ash.

REVIEW OF AEROBIC GRANULAR SLUDGE TECHNOLOGY AND APPLICATION IN WASTEWATER TREATMENT

This paper focuses on introducing an overview of aerobic granular sludge technology, granulation, removal efficiency and application of aerobic granules in wastewater treatment. Aerobic granular sludge has a bacterial layered structure including anaerobic, anoxic and aerobic bacteria in order from inside to outside layer, so it is capable of simultaneous chemical oxygen demand, nitrogen and phosphorus removal. Granular sludge also has capacity to remove persistent organic substances and adsorb heavy metals. As a result, aerobic granular sludge technology can be effectively applied for municipal and industrial wastewater treatment. Many wastewater treatment plants applying aerobic granular sludge technology have been deployed, most commonly in Europe and especially in the Netherlands, which is the first place to apply this technology in practical wastewater treatment with Nereda® trademark. However, aerobic granular sludge is stable on batch reactors and takes months to form stable granular sludge. Therefore, it is necessary to have further researches on the granulation mechanism and affective factors to shorten the time of aerobic granular sludge formation as well as maintain the long-term stability of the granular sludge and develop continuous reactors to maintain the stability of the aerobic granular sludge to meet the requirement of wastewater treatment plants in practice.

Effects of feeding mode on the formation and stability of aerobic granular sludge under combined antibiotic stress

Aerobic granular sludge (AGS) is a promising technology for wastewater treatment due to its high biomass retention, nutrient removal, and resistance to toxic substances. However, the formation and stability of AGS are affected by various factors, such as feeding mode and antibiotic stress. This study investigated how three feeding modes, namely anaerobic plug-flow (APM), anaerobic mixed-flow (AMM), and aerobic feeding mode (AFM), influenced AGS formation and stability under exposure to a mixture of tetracycline, sulfamethoxazole, ofloxacin, and roxithromycin. The results showed that only APM and AMM achieved granulation within 40 d, while AFM failed to form AGS within 90 d due to the low shear force that led to a different composition and structure of extracellular polymeric substances and a high potential barrier calculated by extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. The average granules diameters of APM (896.6 μm) were larger than that of AMM (519.4 μm), and the results of ultrasonic crushing experiment and XDLVO calculation showed that the structural stability of APM was slightly stronger. However, AMM outperformed APM and AFM in terms of total phosphorus removal, antibiotic removal, and long-term operational stability under low temperature conditions. Illumina MiSeq sequencing and qPCR results revealed that typical biofilm formers (Sediminibacterium and env.OPS_17) contributed to the stability of AGS and increased phosphorus accumulating organisms’ genes abundance ensured the high TP removal in AMM. This study offers valuable insights into the effects of diverse feeding modes on aerobic granulation and stability under combined antibiotic stress and suggests that AMM is a promising mode for enhancing AGS performance and resilience in wastewater treatment applications.

Enhancing biofilm growth in an integrated fixed-film activated sludge process through modification of polypropylene carriers

Biofilm is crucial in implementing integrated fixed-film activated sludge (IFAS) systems. However, current carriers face challenges in long-term stable operations. This study proposes using cationic polyacrylamide (PAM) as a positive-charged addictive and surface abrasion to modify polypropylene (PP) pipes to enhance biofilm growth and maintain long-time operation in IFAS applications. The modified PP carriers have significantly increased specific surface area compared to unmodified ones. The growth of biofilm on modified carriers is as much as over four times due to the improved biocompatibility of the material. The follow-up aerobic IFAS process achieves over 40% total nitrogen (TN) removal through simultaneous nitrification and denitrification with no specific anoxic stages or reactors. The sludge settling performance of the system is also improved with a stable 30-min sludge settling ratio of 18%. The maximum specific denitrification rate of the detached biofilm is 17.82 mg NO3−-N/g MLVSS/h, which is 33% higher than the pure activated sludge system. The high-throughput sequencing analysis results reveal that the abundance of biofilm-formation beneficial microbes increased from 0.02% to 16.47%.

Urban sewage sludge stabilization by alkalization-composting-vermicomposting process: Crop-livestock residue use.

Waste management practices are vital for human health and the environment in a world where natural resources stress is expected to increase with the growth of population. Our study aimed to evaluate the potential use of crop-livestock residue as a bulking agent associated with the ideal level of hydrated lime for the stabilization and sanitization of urban sewage sludge through the alkalization-composting process. Therefore, we determined the alkalization efficiency on the heavy metal concentration in urban sewage sludge, quantified the viable eggs of helminths in pure and alkalized sludge, and measured the rate of earthworms (Eisenia fetida) surviving in the vermicomposting process using different levels of alkalized urban sewage sludge associated with crop-livestock residue. Four sequential trials were carried out in a completely randomized design with three replicates. The lime alkalization reduced the levels of Ba, As, Pb, Cu, Cr, Mo, Ni, and Zn compared to the pure urban sewage sludge. Using 30% w/w of lime in the urban sewage sludge (SS-30) for composting process reduced the viable helminth eggs by 71, 72, and 69% for sugarcane bagasse (Saccharum officinarum; SB), fresh chopped Napier-grass (Pennisetum purpureum; NG), and bovine ruminal content (BR), respectively. The ideal level of hydrated lime for stabilization and sanitization of urban sewage sludge was found to be 30%, which was able to reduce the heavy metals. The residues have the potential as a bulking agent for the composting of urban sewage sludge when associated with alkalization. The lime alkalization decreases the total number of helminth eggs and the number of viable eggs. The possibility of starting a vermicomposting using the mixtures is promising, evidenced by the earthworm survival in composting urban sewage sludge mixed with crop-livestock residues after 45 days of composting. The earthworm survival is maintained by an association of at least 80% of the crop-livestock residues.

Long-term operational performance and membrane fouling mechanisms of AGMBR treating municipal wastewater under different superficial air velocities

The granulation and stability of aerobic granular sludge (AGS) as well as membrane fouling in AGS-membrane bioreactor (AGMBR) are significantly influenced by superficial air velocity (SAV). However, there is a lack of relevant research on this topic. Therefore, this study aims to investigate the specific impacts of SAV on AGMBR performance and membrane fouling. The results showed that the experimental SAVs (1.6, 2.1, and 2.6 cm/s) were found to provide sufficient dissolved oxygen for the removal of organics and ammonium nitrogen at efficiencies exceeding 94.50% and 99.40%, respectively. The larger SAV also extended the overall lifespan of the AGMBR, while altering both the content of foulants on fouled membranes and their associated microbial community structure. Moreover, the cake layer exhibiting the highest degree of porosity was observed at an SAV of 2.6 cm/s, which corresponded to the largest pore blocking fouling resistance (28.81% of the total fouling resistance) and the presence of fluorine on the fouled membrane. Additionally, the results from extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory were consistent with the increase in transmembrane pressure. Polysaccharides (PS) played a more significant role than proteins in membrane fouling, and the PS present in soluble microbial products exhibited a strong correlation with fouling resistance distribution. This study aims to optimize the treatment performance and minimize membrane fouling in AGMBR, thereby establishing a mutually beneficial scenario that is essential for the practical implementation of wastewater reuse in engineering.

Positive effects of lignocellulose on the formation and stability of aerobic granular sludge.

Lignocellulose is one of the major components of particulate organic matter in sewage, which has a significant influence on biological wastewater treatment process. However, the effect of lignocellulose on aerobic granular sludge (AGS) system is still unknown. In this study, two reactors were operated over 5 months to investigate the effect of lignocellulose on granulation process, structure stability and pollutants removal of AGS. The results indicated that lignocellulose not only promoted the secretion of tightly bound polysaccharide in extracellular polymeric substances, but also acted as skeletons within granules, thereby facilitating AGS formation, and enhancing structural strength. Lignocellulose imposed little effect on the removal efficiency of pollutants, with more than 95, 99, and 92% of COD, NH4+-N, and PO43--P were removed in both reactors. However, it did exhibit a noticeable influence on pollutants conversion processes. This might be due to that the presence of lignocellulose promoted the enrichment of functional microorganisms, including Candidatus_Accumulibacter, Candidatus_Competibacter, Nitrosomonas, and Nitrospira, etc. These findings might provide valuable insights into the control strategy of lignocellulose in practical AGS systems.