Mixed Sludge Research Articles

Unveiling the Impact of Absorbent Polymers on Self-healing Efficiency of Sludge-derived Capsules in Cementitious Composites

A novel green capsule for self-healing cementitious material using a combination of waste-based materials with an inorganic substance was developed. A mix of alum sludge (AS), a typical waste from the water industry, and calcium hydroxide were used as the primary healing agents. Also, two types of natural and synthetic absorbent polymers (AP), microcrystalline cellulose (MCC) and sodium polyacrylate (SPA), were added to the core mixture to assess their impact on the healing efficiency. The morphology of the produced capsules, the self-healing proficiency of cracked mortars, and the resulting healing materials were characterised. Outcomes revealed that cracks up to 400µm could be healed by the plain capsule. The closure width was dramatically increased to 500µm and 800µm with the inclusion of MCC and SPA, respectively, mainly in 3 days. The expansion, water retention, and bridging properties of the APs enhanced the sealing performance of the capsules by providing nucleation sites and increasing the reaction rates of core materials to generate further calcium-based products inside the cracks. Therefore, higher recovery rates of mechanical strengths, along with a significant reduction in water ingress were achieved. The main healing products were identified as calcite crystals, C-S-H, calcium silicate, and aluminium-bearing phases.

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

Currently, partial nitrification (PN) processes are commonly used to improve efficiency in high ammonia nitrogen wastewaters. However, initiating and restoring damaged PN performance is crucial for optimizing nitrogen removal efficiency without the use of chemical additives. In this study, a simultaneous partial nitrification and denitrification coupled with anammox (SPNAD) sequencing batch biofilm reactor was constructed to treat anaerobic digestion after sludge thermal hydrolysis pretreatment (STHP-AD) filtrate. The PN performance was successfully recovered through optimizing the operation mode of anoxic/oxic alternation within 120 days. Result showed that Nitrosomonas increased from 0.68 % to 3.43 %, while Nitrospira decreased to 0.06 %. The PN recovery also promoted anammox, with the only anammox bacterium of Candidatus Brocadia, detected in the mixing and biofilm sludge of 1.73 % and 1.41 %, respectively. The autotrophic denitrifying bacteria Thermomonas (increasing from 0.47 % to 23.85 %) and Truepera (rising from 2.31 % to 6.54 %) rapidly accumulated. After adjusting to the anoxic/oxic alternation ratio, the hydraulic retention time was shortened from 50 h to 37.5 h, and the oxic time was reduced to half of the initial operation. The PN recovery and anammox enrichment resulted in improving nitrogen removal approximately 20 %. Eventually, the SPNAD system realizes stable and efficient nitrogen removal with the influent nitrogen loading rate of 0.43 kgN/(m3·d), the ammonium removal efficiency of 94.73 ± 3.27 %, and the nitrogen removal efficiency of 72.98 ± 1.27 %. In this study, a new strategy using intermittent aeration while appropriately extending the oxic time was proposed to restore the system’s ability to treat STHP-AD filtrate after PN disruption.

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

This study aims to investigate the conversion of different microbial community compositions in the cathode chamber in a dual-chamber bioelectrochemical system. A denitrifying bacterial community, or sludge, was enriched for denitrification by microbial consortia and subsequently acclimatized within the cathodic chamber of microbial fuel cells, either within a mixed microbial community sludge microbial fuel cell (M-MFC) or a pure culture of microorganisms in a microbial fuel cell (P-MFC). The bioelectrochemical systems were treated with different nitrate concentrations in the cathodic chamber: the MFC with low concentration nitrate (MFC1, 25 mg/L nitrate; MFC2 50 mg/L nitrate), the MFC with medium concentration nitrate(MFC3, 75 mg/L nitrate; MFC4 100 mg/L nitrate), and MFC with high concentration nitrate (MFC5, 125 mg/L nitrate; MFC6 150 mg/L nitrate; MFC7 175 mg/L nitrate), and the initial COD in the anodic chamber was based on demand(C to N ratio is 5). M-MFC exhibited better-electrogenerated capability than P-MFC. However, P-MFC exhibited better nitrogen removal performance compared to M-MFC. The best performance was attained by both types of MFCs when the nitrate content was 100 mg/L. The maximum output voltages in M-MFC4 and P-MFC4 were 449 mV and 171 mV, respectively. The average conversion rate of M-MFC4 and P-MFC4 were 2.9 mg*L−1 *h−1 and 10.5 mg*L−1 *h−1, respectively. The analysis of the microbial community of two treated MFCs in the cathode chamber in the optimal state indicated that non-electrode denitrification predominantly occurs in P-MFC. The cathode chambers were mostly populated by denitrifying microorganisms. The dominant species in M-MFC were Azonexus, Zoogloea, Ignavibacterium, and Pirellula, and the dominant species in P-MFC were Comamonas, Aeromonas, and Acidovorax. The species was assessed by qPCR analysis, and the results validated the use of a bacterial consortium for domestication as a more suitable method to improve the stability and performance of the MFCs.

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

Algal biocathode MFCs (ABMs) are recently being heavily studied due to their advantage over abiotic cathode MFCs (ACMs) as dissolved oxygen (DO) generated by algal growth in the cathodic chamber is directly utilized in cathodic oxidant reduction. In this work growth of pure algae species Scenedesmus obliquus used in the cathode chamber has been studied under a photoperiod of 24 h illumination to supplement oxygen for continual MFC operation without any external supply of air or carbon dioxide and treatment of synthetic wastewater having chemical oxygen demand (COD) equivalent to medium strength domestic wastewater (5.35 g/L COD). Results of ABM showed the highest continuous current density generation of 23.93 mA/m2 and the highest continuous volumetric power density generation of 13.24 mW/m3 were around 120 h with COD removal efficiency of 92.52 % and coulombic efficiency (CE) of 41.88 %. Initial ohmic (Roh) and charge transfer (Rct) resistance values of ABM were found to be 8.3 Ω and Rct of 22.5 Ω which after 216 h of algal growth got reduced to 1 Ω and 15.1 Ω respectively. 16S microbiome profiling of the mixed microbial sludge inoculum used in the anodic chamber showed dominance of Xanthomonadaceae stenotrophomonas (9.7 %), Chitinophaga flexibacter (8.65 %), Sphingomonadaceae sphingomonas (6.82 %), Sphingobacterium multivorum (6.55 %), Dyadobacter fermentans (6.05 %), and Alcaligenaceae achromobacter (5.51 %). Elemental investigation of the bioanode’s and biocathode’s surface carried out using EDS analysis also shows that oxygen was generated in the cathodic chamber by pure Scenedesmus obliquus species.

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

Hydrothermal liquefaction (HTL) is a thermo-chemical method of processing wastewater solids that could be preferential over anaerobic digestion (AD) because it produces a greatly reduced volume of solids. Instead, the effluent can be separated into biocrude refined into fuel, hydrochar a carbon-rich solid and HTL aqueous waste. Unfortunately, HTL aqueous is high in ammonia, phenolics, and nitrogen heterocyclic compounds that can inhibit AD if used for treatment. Ammonia stripping was tested for pretreatment of HTL aqueous from dewatered mixed sludge at 350 °C, 15 min and recovering ammonia. Seven stripping reactor conditions were run, and the best results were seen at 85 °C, a pH of 9.3 and 500 mL/min air flow rate. This case achieved ammonia and total phenolic compounds removal of 79.5 ± 0.1 and 32 ± 1 %, respectively, in 4 h. The ammonia stripping was coupled with acid adsorption to produce an ammonium sulphate salt with fertilizer value. The ideal ammonia stripping conditions produced a salt with a purity of 98.0 ± 0.05 % and represented an ammonia recovery of 73.9 ± 0.04 %. Semi-continuous flow bench-scale thermophilic anaerobic co-digestion of HTL aqueous with municipal sludge found that 12 % of influent chemical oxygen demand (COD) can come from HTL aqueous without inhibition if pretreated with ammonia stripping, while the digester fed with a similar COD from non-pretreated HTL aqueous showed inhibition. Under mesophilic conditions, semi-continuous flow anaerobic co-digestion was successful for non-pretreated and pretreated HTL aqueous even with 24 % and 22 % of influent COD provided by HTL aqueous, respectively.

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

Membrane fouling is still the primary bottleneck issue for the widespread application of anaerobic membrane bioreactor (AnMBR) and quorum quenching (QQ) strategy is one of the feasible approaches for its fouling alleviation. In this study, 2(5H)-furanone was applied as an efficient, cost-effective and non-toxic QSI in a laboratory-scale AnMBR, achieving not only a doubled membrane filtration cycle length but also ensuring relatively stable treatment performance and enhanced methane production. The retarded membrane fouling could result from reduced soluble microbial product (SMP) and extracellular polymer substance (EPS) concentration, decreased by 13.6 % and 26.8 % compared with that in conventional AnMBR. Meanwhile, the biocake morphology also suggest reduced biofilm thickness and less organic deposition on the QQ-AnMBR. The microbial diversity analyses indicated that 2(5H)-furanone addition can accumulate the fermentative and acetogenic bacteria (Propioniciclava, Longilinea and norank_f__Anaerolineaceae in both sludge mix suspensions and biocake) and methanogens (Methanosaeta in bulk sludge, Methanosaeta and Methanobacterium in the biocakes), improving the anaerobic process in AnMBR. Moreover, the relative abundance of norank_f__norank_o__SJA-15, a typical filamentous bacterium and fouling-related microbe, significantly reduced after 2(5H)-furanone addition in the bulk sludge of QQ-AnMBR. Additionally, this study elucidated the membrane fouling control mechanism by 2(5H)-furanone addition through metagenomic and molecular docking analyses. Results indicate that 2(5H)-furanone may control membrane fouling mainly through quorum sensing processes inhibition by (i) competition of 2(5H)-furanone and acyl-homoserine lactones (AHLs) for binding sites on QS receptor proteins, and (ii) quorum quenching with increased lactone enzymes abundance and decreased AHLs concentration. These findings offer valuable insights that can significantly contribute to the advancement of this technology with membrane fouling control.

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.

A short bibliographic review concerning biomethane production from wastewater sludge.

Biomethane production by anaerobic digestion (AD) of sludge from municipal wastewater treatment is a viable practice to valorise the residues of these plants. However, although the relevant literature is abundant, no comprehensive reviews have been recently published on this topic. Detailed information concerning the factors influencing the AD process and values of biomethane production from the sludge from municipal wastewater treatment plants (MWWTPs) on the global scale may support technicians and researchers in both the planning and the design steps of an AD process. This study proposes a systematic review and a meta-analysis of the factors that noticeably influence biomethane yield deriving from AD of sludge from MWWTP. The reported values were systematically analysed compared to the main factors driving AD, including publication year, geographical area of each study, type of digested sludge, treatment in the water line of the MWWTP, possible sludge pre-treatments, type of digestion process, hydraulic retention time (HRT) and temperature regime of the AD process. A higher biomethane production was registered in North American plants compared to countries in other continents. Older studies published between 2001 and 2005 reported lower mean values compared to the more recent experiments. A gradient of 'primary sludge' > 'mixed sludge' > 'wastewater activated sludge' was found for the mean biomethane yield in relation to the digested sludge type. The mean biomethane yields for different types of sludge on a global scale are 0.425, 0.296 and 0.176 Nm3 kg VS-1 for primary sludge, mixed sludge and waste activated sludge, respectively. Overall, the study demonstrates: (i) the very large variability of biomethane yields from AD of the residues from MWWTPs (mainly due to the different characteristics of sludge) and (ii) the non-significance of some factors (i.e. treatment in the water line, pre-treatments, type of process, HRT and temperature regime) on energy yields from the AD process.

Withdrawn: Co-hydropyrolysis of sewage sludge and algae biomass: A systematic study on thermal decomposition behaviors and kinetic characteristics

In the present study, a thermogravimetric analyzer was used to assess the co-hydropyrolysis kinetics of sewage sludge and algae biomass. Three isoconversional methods (Kissinger-Akahira-Sunose, Flynn-Wall-Ozawa, and Friedman) and one model-fitting method (DAEM) accurately fitted the experimental data at three heating rates (10, 30 and 50 °C/min) between 10 % and 90 % conversion. These methods agree with the trends shown by the activation energy (Ea) distribution calculated, with fluctuations between 120 and 330 kJ/mol. Compared with the pyrolysis of a single sample, the reaction activation energy of sludge and algae was significantly reduced in the case of co-pyrolysis. When 20 % algae are added, the activation energy is only 50 % of the original, below 100KJ/mol. Physiochemical characterization confirmed that they have the potential for fuel and energy production. Kinetic parameters fitted by DAEM were successfully verified at the highest heating rate studied and the linear fitting curve of DAEM is better. The kinetic results confirm that the activation energy is related to the conversion rate, and the change of activation energy and conversion rate indicates that the biomass undergoes a very complex pyrolysis process. In this study, the mixing of sewage sludge and algal biomass in hydrogen atmosphere can significantly change the energy required for pyrolysis reaction, which provides data support for the development, design and optimization of pyrolysis reactors. According to the change of weight loss and activation energy, it provides support for the feed amount, reaction temperature and gas flow of the pyrolysis furnace in the process of pyrolysis reaction.

Evaluation of Hospital Wastewater Treatment Using Sewage Treatment Plant for Heavy Metals, Radionuclides, and Some Pharmaceuticals: A Case Study

This is the first study in Oman to evaluate the efficiency of a sewage treatment plant (STP) for hospital wastewater (HWW) treatment for heavy metals, radionuclides, and some selected pharmaceuticals. A sewage treatment plant (STP) at Sultan Qaboos University (SQU) receives HWW, from Sultan Qaboos University Hospital (SQUH), and municipal wastewater from non-medical facilities at SQU. Representative samples of HWW (before mixing with municipal wastewater at STP), STP-treated wastewater (TWW), and STP mixing sludge, were collected and analyzed. A method for analyzing pharmaceuticals including metformin, atenolol, chlorpheniramine, triprolidine, diphenhydramine, and citalopram was developed and validated using LC-MS-MS. HWW and TWW show low concentrations of heavy metals. Radionuclides found in HWW include Cs137, K40, Ra226, Th234, I131, Tl208, Zn65 Ac228, Sb125, Bi124 and Be7. Diphenhydramine (2.24 mg/L), chlorpheniramine (0.293 mg/L) and atenolol (0.0260 mg/L) were found in HWW. Heavy metals, radionuclides, and pharmaceuticals were found less in TWW than in HWW. STP sewage sludge showed higher levels of these pollutants than HWW or TWW. Concentrations of diphenhydramine, chlorpheniramine, and citalopram were 137, 0.950, and 169 mg/kg, respectively in dried sewage sludge. The study confirms the ineffectiveness of STP treatment to completely remediate HWW. HWW should be considered hazardous and requires physico-chemical treatment before mixing with municipal wastewater. Keywords: Hospital, pharmaceuticals, radionuclides, heavy metals, wastewater.

Pulp mill sludges as a solution for reducing the risk of mineral nitrogen leaching from agriculture

Nitrogen (N) from agricultural systems contributes to the eutrophication of waterbodies through leaching. Incorporating organic material with a high carbon-to-nitrogen (C/N) ratio, such as mixed pulp mill sludges (PMSs), into the soil in autumn could reduce the amount of leachable N. This study tested the potential of composted and lime-stabilised mixed PMSs (CPMS and LPMS) in reducing the concentration of mineral N in the soil, and thus the risk of N leaching from arable land in the boreal region using a two-year field experiment. To better understand the mechanisms of the PMSs for influencing mineral N concentration in soil, the impact of PMSs with different quality on the reactions of N in the soil was investigated in a laboratory incubation study. In the field experiment, nitrate-N (NO3--N) concentration was lower with PMSs compared to mineral fertilisation and the control during the first autumn and the following spring after PMS application. The undersowing of Italian ryegrass reduced the NO3--N concentration in the soil during the first autumn. In the incubation experiment, PMSs reduced the soil ammonium-N (NH4+-N) concentration at the beginning of the experiment and the soil NO3--N concentration throughout the experiment compared to a mineral fertiliser treatment and an organic fertiliser. Increased soil respiration in PMS-treated soils indicated increase in microbial activity, and thus immobilisation of soil NO3--N and NH4+-N due to PMSs addition. These results suggest that PMSs have the potential to reduce N leaching from agricultural soils. However, the immobilisation of N must be considered when planning the nutrient requirements of the following crops.

Evaluating drained water quality in a pilot worm-sludge treatment reed bed planted with Arundo donnas in the Mediterranean climate

This study evaluated the impact of incorporating earthworms (Eisenia fetida) on the drained water quality from a sludge treatment reed bed. The experiment encompassed four setups of treatment beds in two replicates: planted with Arundo donax and addition of earthworms, planted without earthworms, unplanted with earthworms, and treatment bed without plants nor earthworms as control. The units were fed every two weeks with mixed sewage sludge, a blend of primary and secondary sludge over 24 cycles. The mixed sewage sludge had mean dry and volatile solid contents of 24.71 g.DS.L−1 (± 13.67) and 19.14 g.VS.L−1 (± 10.29) resulting a sludge loading rate of 43.59 kg.DS.m−2.year−1 (± 14.49). The inclusion of earthworms in the planted unit reduced release masses of total suspended solids, chemical oxygen demand, nitrate and phosphorous by 43, 45, 75 and 45 % compared to the planted unit. Plant biomass production increased by 43 % with the earthworm presence. The removal efficiency of the units improved after a ramp-up phase (after six months feeding) of which the concentration of TSS, COD and Escherichia coli met limits for water reuse while nitrogen components and phosphorous surpassed the limits. The planted unit with earthworms removed 99 and 99 % of TSS and COD, respectively. Overall, water loss namely through evapotranspiration and earthworm hydration need, positively correlated with pollutant concentration, and earthworm-planted unit had 46 % higher water loss compared to control unit.

Anaerobic mono-digestion and co-digestion of food waste and mixed sewage sludge: A comparative analysis of metabolic patterns and taxonomic profiles

This study systematically compares the anaerobic mono-digestion and co-digestion of food waste (FW) and sewage sludge to understand the effects of feedstock composition on biogas yield and microbial community structure. The results showed that FW mono-digestion is optimal for methane production, achieving a peak yield of 377.25 ± 29.55 mL/g volatile solids fed (VSfed) but also generated significant quantities of hydrogen (151.59 ± 1.35 mL H2/g VS) during initial hydrolysis and acidogenesis phases. In contrast, waste-activated sludge (WAS) mono-digestion results in significantly lower methane yields (206.63 ± 1.18 mL/g VSfed). However, co-digesting FW with WAS enhances process stability, reducing the lag phase duration, albeit with an 8 % decrease in methane production relative to the theoretical potential. Further, it was observed when WAS was co-digested with primary sludge (PS), leading to a 34 % increase in methane yield compared to WAS mono-digestion. Soluble protein breakdown was highly efficient in WAS and PS treatments, exceeding 80 %, while FW treatments achieved less than 14 % degradation. Taxonomic analysis revealed a dominance of Firmicutes, specifically Clostridium sensu stricto 1, in FW reactors, whereas WAS and PS reactors supported a more diverse microbial community structure. Enzyme analysis indicated an upward trend in cellulase activity in WAS and PS reactors over time. These insights emphasize the importance of selecting appropriate feedstock combinations to enhance methane production, offering a pathway to more efficient anaerobic digestion processes and improved biogas recovery from organic waste.

Anaerobic co-digestion of municipal mixed sludge and mango peel biowaste: Performance and stability analysis for different ratios

In an urban context, municipal mixed sludge (MMS) and fruit and vegetable waste (FVW) are becoming the major organic solid wastes in human society. Thus, anaerobic digestion as a low carbon energy strategy to minimize their environmental polluting risk was studied. To overcome the drawbacks of anaerobic digestion of MMS, an alternative approach is proposed, involving the addition of increasing proportions of mango peel pulp (MPP) as a co-substrate. Different ratios of MMS:MPP (v:v) were studied: 80:20 (T1), 70:30 (T2), 60:40 (T3). The increase in the organic loading rate was well incorporated by the reactor's biomass activity, and it had no negative effects on the reactor stability and performance operational parameters. Results indicated that the addition of MPP had a beneficial effect on specific methane production, where the highest value was registered in T2 (0.47 L CH4/g VS added), with a 1.8-fold increase in this operational parameter. Moreover, bioenergy recovery within the same trial followed the same profile, representing a two-fold increment.

Improved Production of Marandu Palisade Grass (Brachiaria brizantha) with Mixed Gelatin Sludge Fertilization

Gelatin industry residues are increasingly used as fertilizer and soil conditioner. However, correct residue dosage is critical for grass development and minimizing environmental impacts. This randomized block design study determined adequate dosage of mixed gelatin sludge (MGS) for Marandu grass production in wet/dry seasons in Brazil. Five MGS levels (0–200% of required nitrogen) were compared to mineral fertilizer. Agronomic/productivity characteristics, bromatological composition, macro/micronutrient composition of leaves, and soil chemical attributes were evaluated. Agronomic/productivity characteristics were influenced by MGS dose in both dry/rainy seasons, except for leaf blade pseudostem ratio and percentage of leaves/pseudostem. Bromatological composition was influenced by MGS doses in dry/rainy seasons except for dry/mineral material quantities. Marandu leaf tissue chemical composition was significantly influenced by MGS dose, except for potassium, boron, and iron. Chemical composition of four soil layers between 0 and 50 cm influenced MGS dose, except for pH, organic matter, magnesium, copper, manganese, and zinc. GMS dose for Marandu production should be 200% of nitrogen requirement. MGS application increased productivity/quality of Marandu grass. Macronutrients (nitrogen, phosphorus) and micronutrients (calcium, magnesium, sulfur, copper, and zinc) increased in Marandu grass and in the soil (calcium, sulfur, and sodium). The increased sodium level was not limiting.