Mixed Sludge Research Articles

Mesophilic anaerobic digestion of mixed sludge in CSTR and AnMBR systems: A perspective on microplastics fate.

Most microplastics (MPs) end up in the biosolids produced in wastewater treatment plants (WWTPs) and can pose contamination risks when the biosolids are applied to agriculture. This study evaluated the impact of mesophilic anaerobic digestion on the fate of MPs in WWTP sludge. For this, two laboratory-scale anaerobic digesters were operated in parallel, consisting of a continuous stirred tank reactor (CSTR) and a membrane bioreactor (AnMBR) equipped with an ultrafiltration membrane to decouple the hydraulic and sludge retention times. Both digesters were continuously fed with mixed sludge from a municipal WWTP. The results showed a significant reduction in the MP concentration, with the AnMBR having the higher MP removal efficiency (88.6% vs. 62.1%) and obtaining a higher percentage of biomethanisation (58.3% vs. 43.7%). Polypropylene (PP) and polyacrylonitrile were the main polymers in the mixed sludge, while PP and polyethylene were the dominant polymers in the digested samples. The MP particles in all the samples were predominantly in the 500-104μm size range. Microbiological analysis indicates a greater species diversity in the microbial community of the AnMBR, the results also revealed a symbiotic relationship between the Firmicutes and Patescibacteria phyla in this digester.

Anaerobic co-digestion of hydrothermal liquefaction of aqueous phase with municipal sludge and dewatering centrate.

For integrating hydrothermal liquefaction (HTL) of sludge treatment to municipal wastewater treatment plants, this study demonstrated the feasibility of thermophilic (55°C) anaerobic co-digestion of liquid product of HTL (HTL aqueous) with municipal sludge and its dewatering centrate. Seven semi-continuously fed digesters were operated for a total of 420 days. To obtain an optimal mixing ratio of the HTL aqueous with other co-substrates, a wide range of parameters were tested on influent and effluent of the digesters with 0.0%-43.3% of the chemical oxygen demand (COD) loading rate of the co-digesters contributed by HTL aqueous. HTL aqueous was generated from mixed sludge (20% total solids) at 350°C, 170bar, and 20min retention time. Thermophilic co-digesters with HTL aqueous contributing to 12.0%, 23.1%, and 43.3% of the total COD load were fully inhibited after 42, 29, and 15 days, respectively, while co-digesters with 1.21% and 2.74% of total COD contribution by HTL aqueous operated without any inhibition over 180 days. Biogas production in the co-digester with 4.89% COD contribution from HTL aqueous was also inhibited after 95 days of operation. This co-digester experienced a complete process failure for 42 days, followed by 218 days of partial (76%) steady inhibition before fully recovered. This indicates that thermophilic cultures can acclimatize to inhibitors in HTL aqueous to a certain extent. High levels of nitrogen heterocyclic compounds, such as pyridines and pyrazines, in HTL aqueous were determined to be the cause of inhibition in co-digesters fed with high volume of HTL aqueous. This study demonstrated the feasibility of valorizing HTL aqueous from mixed sludge in thermophilic co-digesters with a COD contribution as high as 4.89% from HTL aqueous.

Integrating renewable energy in sewage sludge treatment through greenhouse solar drying: A review.

Sewage sludge is the main by-product of wastewater treatment plants, requiring significant environmental and economic burdens for its management and disposal. Recently, solar drying processes, often performed through solar greenhouses, received interest due to their limited energy requirement and renewable energy exploitation. The dried sludge shows significant volume and mass reductions, reducing transportation and disposal costs. However, its physicochemical and microbiological characteristics must be properly assessed, especially if agricultural reuse is the final sludge destination, due to the possible accumulation of (micro)pollutants in the soil. This review depicts the state-of-the-art solar drying processes of sewage sludge, with a focus on the technological aspects and the sludge quality. The review discusses greenhouse-specific features, sludge composition (organic matter, pathogens, heavy metals and emerging pollutants) and drying conditions (seasonality, ventilation, sludge mixing and thickness, and drying speed). The economic aspects connected to sludge solar drying are presented. The limitations of this technology are discussed as well, including the limited applicability to wet sludge and the environmental issues connected to greenhouse structure degradation. A wider application of sludge solar drying is recommended to increase the sustainability of small and medium wastewater treatment plants, especially in areas with high amounts of solar radiation and dry weather conditions, while thermal drying still appears preferable for large plants. More agronomic studies must be conducted to assess the possible pollutant accumulation in crops, and alternative uses of the dried sludge (e.g., energy recovery through incineration, pyrolysis or gasification; utilization in construction materials) should be explored, also using life cycle assessment.

Enhanced anammox cultivation using mixed sludge and optimized nitrite- ammonium ratio

Enhanced anammox cultivation using mixed sludge and optimized nitrite- ammonium ratio

Biomethane Production Through Performance Enhancement of Anaerobic Digestion and Sludge Dewatering Processes in a Wastewater Treatment Plant

Sewage sludge management poses a persistent challenge due to increasing volumes and stringent environmental regulations. Current municipal wastewater treatment technologies are energy intensive, produce large quantities of residuals and fail to recover the potential resources available in wastewater. Anaerobic digestion (AD) is widely recognized for its cost-effective stabilization, high organic matter removal, and biogas production potential. However, the hydrolysis phase remains a bottleneck in AD, limiting methane yield. Furthermore, its application for low strength municipal wastewater is limited. To address such challenges, the effects of combined microwave-ultrasonic and combined microwaveoxidative pre-treatment of thickened excess activated sludge and mixed sludge on the performance enhancement of conventional mesophilic digester and on two-stage digesters are presented in this study. Microwave-ultrasonic pretreatment was optimized for enhanced cell disruption, while microwave oxidation pretreatment incorporated hydrogen peroxide to generate reactive oxygen species for accelerated organic solubilization. Experimental setups included single- and two-stage anaerobic digesters operated under mesophilic and thermophilic conditions. Results demonstrated that combined microwave-ultrasonic pretreatment improved cumulative methane production by 18% and total solids reduction by 31%, compared to microwave-only pretreatment. Microwave oxidation pretreatment with 1% H₂O₂ achieved 40% volatile solids solubilization, significantly enhancing methane yield and sludge dewaterability. The two-stage AD process further improved performance, achieving 76.4 mL/g TCOD methane yield and 58% methane content in biogas, outperforming single-stage systems. Findings indicate that hybrid pretreatments synergistically enhance hydrolys

Evaluating the Performance of Anaerobic Digestion with Upstream Thermal Hydrolysis—What Role Does the Activated Sludge Process Play?

The performance of anaerobic digestion of mixed sludge (MS) with upstream thermal hydrolysis of waste activated sludge (WAS) was evaluated and compared to conventional anaerobic digestion. In contrast to previous studies, this work focuses on the evaluation of the impact of the activated sludge process, which was assessed using a temperature-normalized solids retention time (SRTASP,T). For this purpose, data from a full-scale wastewater treatment plant related to SRTASP,T, primary sludge (PS) and WAS production were combined with experimental data from laboratory-scale anaerobic digestion of PS, WAS, thermally hydrolyzed WAS, and MS. The parameter SRTASP,T was used as a key link between the full-scale and experimental data. For WAS, SRTASP,T essentially influenced the efficacy of thermal hydrolysis on the performance of anaerobic digestion. The increase in methane yield was higher with increasing SRTASP,T. When considering MS, however, the increase was significantly lower and leveled out over the investigated range of SRTASP,T, mainly due to corresponding WAS/MS ratios. This study demonstrates that the knowledge of SRTASP,T, sludge production, and anaerobic degradability enables the assessment of the potential of thermal hydrolysis and its effect on anaerobic digestion.

Bioplastic’s Valorisation by Anaerobic Co-Digestion with WWTP Mixed Sludge

Bioplastics are designed to degrade at the end of their lifecycle, but effective management of their end-of-life phase and integration into existing organic waste management systems remain significant challenges. Some bioplastics decompose under anaerobic conditions, with the anaerobic digestion (AD) process being a potential solution for their disposal. AD is a promising technology for valorising organic wastes, enabling biomethane production, reducing carbon footprints, and promoting product circularity. This study focuses on evaluating the continuous co-digestion of bioplastics with mixed sludge from an urban wastewater treatment plant (WWTP). Polyhydroxybutyrate (PHB) was the selected bioplastic, as various studies have reported its high and rapid degradation under anaerobic mesophilic conditions. PHB’s biodegradability under typical WWTP anaerobic digestion conditions (35 °C, 20-day retention time) was assessed in batch tests and the results indicate that PHB degradation ranged from 68 to 75%, depending on particle size. To further explore the potential of AD for PHB valorisation, the feasibility of anaerobic co-digestion of PHB with WWTP sludge was tested on a continuous laboratory scale using two digesters: a conventional digester (CSTR) and an anaerobic membrane bioreactor (AnMBR). The results indicated complete degradation of PHB, which led to higher biomethanisation percentages in both digesters, rising from 58% to 70% in the AnMBR and from 44% to 72% in the CSTR. The notable increase observed in the CSTR was attributed to changes in microbial populations that improved sludge biodegradability.

Improving in-situ biomethanation of sewage sludge under mesophilic conditions: Performance and microbial community analysis

Improving in-situ biomethanation of sewage sludge under mesophilic conditions: Performance and microbial community analysis

Optimizing anoxic/oxic intervals in intermittent aeration for STHP-AD filtrate treatment: Restoring partial nitrification and community dynamics in the SPNAD system

Optimizing anoxic/oxic intervals in intermittent aeration for STHP-AD filtrate treatment: Restoring partial nitrification and community dynamics in the SPNAD system

Unveiling the impact of absorbent polymers on self-healing efficiency of sludge-derived capsules in cementitious composites

Unveiling the impact of absorbent polymers on self-healing efficiency of sludge-derived capsules in cementitious composites

The bio-cathode of microbial fuel cells systems: Performance analysis under different microbial community conditions

The bio-cathode of microbial fuel cells systems: Performance analysis under different microbial community conditions

A comparative study of worm-sludge treatment reed bed planted with Phragmites australis and Arundo donax in the Mediterranean region

Sludge treatment reed bed planted (STRB) with Phragmites australis (P.australis) and Arundo donax (A.donax) was assessed in the presence of Eisenia fetida under control condition during the dry season. Worm-planted units were fed with mixed sewage sludge (dry and volatile solids of 29.44 g DS.L−1 and 24.23 g VS.L−1). Sludge loading rates (SLR) of 50, 60, and 70 kg DS m−2 year−1 were examined to assess dewatering efficiency. Surface layers in units with P.australis and A.donax achieved DS of 80 and 81% at a loading rate of 50 kg DS m−2 year−1, while their subsurface DS were 41 and 25%, respectively. Units with A.donax experienced plant loss when subjected to SLR exceeding 60 kg DS m−2 year−1. More than 10 cm of residual sludge accumulated on the top of units after a 2-month final rest. Evapotranspiration was greater in the unit with P.australis (5.23 mm day−1) compared to the unit with A.donax (4.24 mm day−1) while both were fed with 70 kg DS m−2 year−1. Water loss contributions from residual sludge layer, drained water, and evapotranspiration were 3, 46, and 51%, respectively. Units with P.australis indicated 20% higher water loss compared to units with A.donax. Although the drained water quality improved over time, it did not meet standard limits. The residual sludge layer contained macro and micronutrients, and heavy metals with a significant elemental order of N > Ca > P > S > mg > K (N:P:K = 31:8:1), Fe > Na > B > Mn > Mo and Zn > Cr > Cu > Pb > Ni > Cd. Overall, STRB could be a sustainable alternative technology to conventional sewage sludge management techniques.Graphical

Life Cycle Assessment and Net Energy Analysis of an Integrated Hydrothermal Liquefaction-Anaerobic Digestion of Single and Mixed Beverage Waste and Sewage Sludge

The conversion of biomass to bioenergy is one of the approaches to creating a sustainable society. In this study, the life cycle assessment and the net energy analysis of converting mixed sewage sludge and beverage waste into bioenergy via a combined hydrothermal liquefaction-anaerobic digestion (HTL-AD) system was carried out. Primary sludge (PS), winery rose lees (RL), brewery Trub (BT), the mixture of brewery trub and primary sludge (BTPS) and the mixture of winery rose lees and primary sludge (RLPS) were the feedstocks considered. Efficient energy utilization [in form of net energy ratio (NER)], and environmental emissions were evaluated. The NER of BT (2.07) and RL (1.76) increased when mixed with PS (3.18) to produce BTPS (3.20) and RLPS (2.85). Also, the HTL phase of the combined HTL-AD system produced a greater NER than the AD phase in BT, BTPS, and PS and vice-versa in RL and RLPS. Six environmental impact categories were studied namely global warming, terrestrial acidification, ionizing radiation, terrestrial ecotoxicity, human carcinogenic toxicity, and human non-carcinogenic toxicity. RL produced the greatest environmental impact while BTPS produced the least impact, thus indicating the advantage of feedstock combination. This study shows that the combination of feedstocks for bioenergy production in an HTL-AD system does not only increase the quality and quantity of products but also increases the overall NER as well as reducting the environmental impacts. The study also proved that an integrated HTL-AD system is an energy efficient system with greater resource utilization and less environmental footprint than the constituent systems.

Simultaneous organic wastewater treatment and bioelectricity production in a dual chamber microbial fuel cell with Scenedesmus obliquus biocathode

Simultaneous organic wastewater treatment and bioelectricity production in a dual chamber microbial fuel cell with Scenedesmus obliquus biocathode

Ammonia recovery via stripping from hydrothermal liquefaction aqueous from sludge for anaerobic co-digestion pretreatment

Ammonia recovery via stripping from hydrothermal liquefaction aqueous from sludge for anaerobic co-digestion pretreatment

Pilot-scale evaluation of cascade anaerobic digestion of mixed municipal wastewater treatment sludges.

This work assessed the performance of a pilot-scale cascade anaerobic digestion (AD) system when treating mixed municipal wastewater treatment sludges. The cascade system was compared with a conventional continuous stirred tank reactor (CSTR) digester (control) in terms of process performance, stability, and digestate quality. The results showed that the cascade system achieved higher volatile solids removal (VSR) efficiencies (28-48%) than that of the reference (25-41%) when operated at the same solids residence time (SRT) in the range of 11-15 days. When the SRT of the cascade system was reduced to 8days the VSR (32-36%) was only slightly less than that of the reference digester that was operated at a 15-day SRT (39-43%). Specific hydrolysis rates in the first stage of the cascade system were 66-152% higher than those of the reference. Additionally, the cascade system exhibited relatively stable effluent concentrations of volatile fatty acids (VFAs: 100-120 mg/l), while the corresponding concentrations in the control effluent demonstrated greater fluctuations (100-160 mg/l). The cascade system's effluent pH and VFA/alkalinity ratios were consistently maintained within the optimal range. During a dynamic test when the feed total solids concentration was doubled, total VFA concentrations (85-120 mg/l) in the cascade system were noticeably less than those (100-170 mg/l) of the control, while the pH and VFA/alkalinity levels remained in a stable range. The cascade system achieved higher total solids (TS) content in the dewatered digestate (19.4-26.8%) than the control (17.4-22.1%), and E. coli log reductions (2.0-4.1 log MPN/g TS) were considerably higher (p < 0.05) than those in the control (1.3-2.9 log MPN/g TS). Overall, operating multiple CSTRs in cascade mode at typical SRTs and mixed sludge ratios enhanced the performance, stability digesters, and digestate quality of AD. PRACTITIONER POINTS: Enhanced digestion of mixed sludge digestion with cascade system. Increased hydrolysis rates in the cascade system compared to a reference CSTR. More stable conditions for methanogen growth at both steady and dynamic states. Improved dewaterability and E. coli reduction of digestate from the cascade system.

Effective sludge management: Reuse of biowaste and sewer sediments for fired bricks

ABSTRACT This study partially replaced the clay with sewer sludge (SS) and rice husk (RH-SS) to make fired bricks. The brick samples were examed in terms of shrinkage, water absorption, and compressive strength. Besides, they were analyzed via XRD and metal extraction to determine the heavy metal residuals in the products. The results showed that it was possible to fabricate fired bricks using sewer sludge or rice husk-blended sludge with up to 30% by weight. These brick samples complied with the technical standard for clay brick production, in which the compressive strength was more than 7.5 MPa, water absorption was from 11–16%, and the linear shrinkage was all less than 5%. The rice husk addition helped mitigate the heavy metal residuals in the bricks and leaching liquid, in which all the values were lower than the US-EPA maximum concentration of contaminants for toxicity characteristics. Implications: Previous studies have proved the possibility of mixing sewage sludge from different origins (sewage sludge, river sediment, canal sediment, sewer sediment, etc.) with clay and some wastes to make bricks. In which, mostof the studies used sewage sludge from wastewater treatment plants, very fewdealt with lake/river or sewer sediment. This study shall be the first to study the possibility of employing sewer sediments with the addition of rice husk powder to achieve two targets, including (1) the reuse of biowaste and sludge for brick fabrication and (2) the reduction of heavy metals in final calcined bricks. Different ratios of the rice-husk blended sewer sludge (RH-SS) – clay mixture shall be tested to find the optimized compositions. The results showed that it was possible to fabricate fired bricks using sewer sludge or rice husk-blended sludge with up to 30% by weight, which meant reduce 30% of clay in the brick production. The final products were proved to meet the quality standard in terms of compressive strength (more than 10 MPa), water absorption(from 11–16%), and the linear shrinkage (less than 5%). Larger scale of this study can be an evident to recommend for policy change in the waste reuse in construction field.

Alternatywne podejście do usuwania/odzyskiwania wybranych metali z wody kopalnianej wypływającej z zalanej kopalni syderytu Nižná Slaná

The objective of this work was the application of innovative method for metals recovery from metalliferous mine water released from the flooded siderite ore deposit Nižná Slaná. Although the metals contained in mine drainage are considered environmental pollutants, they may also be recognised as valuable resources. Several techniques can be used to obtain them by precipitation. Conventional processes using alkaline reagents produce huge amounts of mixed sludge with appropriate storage and management requirement, void of possibility of individual metals subsequent processing. This study examined the feasibility of Fe and Mn selective retrieval from real mine water. After oxidation and partial precipitation of iron using hydrogen peroxide, precipitation by sodium hydroxide was applied to the residue iron removal from mine water. In the next step potassium permanganate was used to eliminate manganese by oxidative precipitation. ORP and pH values of processed mine water was recorded in the course of oxidation/precipitation processes. The morphology and elemental composition of obtained products were studied by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The recovery efficiencies of Fe and Mn from mine water reached 99.87 % and 99.25%, respectively. Target metals were removed with high selectivity to levels that comply with environmental requirements.

Exploring the mechanism of membrane fouling alleviation with furanone and its derivatives addition as quorum sensing inhibitors

Exploring the mechanism of membrane fouling alleviation with furanone and its derivatives addition as quorum sensing inhibitors

Research on the toxic effects of polyacrylamide and cadmium on plants during soil utilization of municipal sludge

AbstractThis research aimed to examine the compound effects of polyacrylamide (PAM) and cadmium (Cd) on plant growth subsequent to the mixing of municipal sludge with soil and to explore the potential ecological risks associated with the use of sludge. A pot experiment was performed wherein four gradients (0, 5, 15, and 20 g/[kg dry sludge]) were established corresponding to different PAM concentrations to assess the effects on the physiological and biochemical parameters of Brassica campestris L. ssp. chinensis Makino and Brassica campestris L. and the effects on Cd and PAM concentrations in soil. The findings indicated that the biomass of both plants increased when the total PAM concentration ranged from 5 g to 15 g/(kg dry sludge). Concurrently, polyacrylamide (PAM) downplayed the uptake of Cd by the plants, reduced phytotoxicity, and increased the activities of antioxidant enzymes such as superoxide dismutase (SOD) and peroxidase (POD) in the roots. However, the biomass of Brassica campestris L. ssp. chinensis Makino and Brassica campestris L. decreased significantly when the total PAM concentration was exceeded 15 g/(kg dry sludge), and the toxic effect of Cd on pants was enhanced to some extent. Especially when the PAM concentration was 20 g/(kg dry sludge), apparent cell damage was observed in root cells. It was further noted that Brassica campestris L. portrayed a higher tolerance towards higher proportions of sludge compared with Brassica campestris L. ssp. chinensis Makino. Sludge holds a wider scale of applicability in landscaping than in agriculture. A fusion of polyacrylamide (PAM) and antioxidant enzymes could potentially counteract the effects of Cd within a specific concentration range, serving as a defense mechanism against stress. The data obtained from this study are crucial for unraveling anti‐stress responses and detoxification mechanisms employed by different plant species under the influence of factors such as PAM, Cd, and others, thus providing novel insights into research related to land use involving sludges.