Influence of humic substances on bioavailability of Cu and Zn during sewage sludge composting

Influence of humic substances (HS) on bioavailability of Cu and Zn was characterized during 120 days co-composting of sewage sludge and maize straw. At the initial stage of composting, Cu and Zn in sewage sludge were released as organic matter was degraded, and water soluble Cu and Zn increased markedly. Water soluble Cu and FA content decreased after 21 days whereas water soluble Zn increased during the whole process. Both HA-Cu and HA-Zn were significantly and positively correlated with HA and H/F, respectively. At the end of composting, the distribution coefficients of HA-Cu and HA-Zn reached 27.50% and 3.33% respectively with HA-Cu/HA-Zn ratio increased from 1.29 to 2.73. The results suggest that Cu combined with HA more strongly than Zn, and composting treatment could decrease bioavailability of Cu markedly.     

How does storage affect the quality and quantity of organic carbon in sewage for use in the bioremediation of acidic mine waters?

Pit lakes (abandoned flooded mine pits) represent a potentially valuable water resource. However, acid mine drainage (AMD) generation due to mining activities often results in pit lake waters with low pH, high sulphate and dissolved metal concentrations. Sulphate reduction-based bioremediation offers tremendous scope for removal of acidity and metals from pit lake water. In this study, the effect of storing sewage on its carbon quality for bioremediation of acidic pit lake water was studied. In addition, the effectiveness of labile organic carbon (lactic acid and ethanol) on SRB activity was tested. Bioremediation experiments were performed in controlled and replicated microcosms with acidic (pH 2.2) water from a pit lake by addition of stored (3 years at 4 °C) sewage for stimulation of sulphate reducing bacteria (SRB) activity. This sewage had been previously used successfully in remediating to pH 7 water from this pit lake. The initial aim was to test the sewage at lower doses (18 and 28 g/L) and in a pulsed addition (over 5 weeks). Bioremediation efficacy was evaluated by measuring pit lake water pH increase, redox potential decrease, and acidity and sulphate removal. Though the stored sewage had retained a very similar high total organic carbon (TOC) equivalent to prior to storage, it failed to increase dissolved organic carbon (DOC) levels in pit lake water. Microcosms amended with doubled doses of sewage and an extended remediation time still failed to demonstrate any substantial improvement in water quality, other than a small amount of sulphate reduction and direct neutralisation by the sewage. In order to determine if low DOC concentrations in sewage were the cause of the bioremediation failure, labile organic carbon (LOC), consisting of 50:50 (w/w) lactic acid and ethanol, was added to all microcosm treatments at concentrations of 3000, 6000 and 9000 mg/L. After LOC addition, water quality improved with effective removal of acidity, sulphate and metals in the lowest carbon concentration (3000 mg/L). However, 6000 and 9000 mg/L LOC concentrations showed a delay in response due to the increased acidity associated with the lactic acid addition. The experiments showed that pulsed dosing of carbon simply slowed the commencement of remediation but it was ultimately able to reach the same effectiveness as the equivalent quantity added all at once. Prolonged storage of sewage leads to loss of LOC. In situ pit lake remediations which aim to make use of sewage as the main carbon source will need to factor in the storage time required to obtain sufficient sewage for the treatment into the design. Pulsing may help reduce issues with storage or supplementation with LOC may need to be considered. Results highlight that LOC is a more useful indicator of material effectiveness compared to a simple measures of TOC.     

Remediation of chromite ore processing residue by pyrolysis process with sewage sludge

The present work developed a novel technique to treat chromite ore processing residue (COPR). The process involved mixing the COPR with sewage sludge followed by pyrolysis. The gaseous organic fraction generated during pyrolysis of sludge was beneficial to Cr(VI) reduction. Process variables, such as the amount of sludge added to COPR (sludge-to-COPR (S/C) ratio), heating temperature, reaction time and particle size, were systematically varied, and their influences on the Cr(VI) reduction in COPR were investigated. Cr(VI) content had decreased greatly, from 3384 mg kg⁻¹ for untreated COPR to less than 30 mg kg⁻¹ for COPR treated at 600 °C.     

Co-digestion of intermediate landfill leachate and sewage sludge as a method of leachate utilization

This study examines the co-digestion of intermediate landfill leachate and sewage sludge from a municipal wastewater treatment plant. Application of leachate as a co-fermentation component increased the concentrations of soluble organic compounds (expressed as total organic carbon), ammonium nitrogen, and alkalinity in the digester influents.The biogas yield obtained from the co-fermentation of a 20:1 sewage sludge: intermediate leachate mixture was 1.30 m³ per kg of removed volatile solids (VS), while that from a 10:1 mixture was 1.24 m³ per kg of removed VS. These values exceeded the biogas yield for the sludge alone by 13% and 8%, respectively. The leachate addition influenced the proportion of methane to a minor extent. Increased methane yields of 16.9% and 6.2% per kg of removed VS were found for the two sewage sluge:intermediate leachate mixtures, respectively.     

Treatment of fresh leachate with high-strength organics and calcium from municipal solid waste incineration plant using UASB reactor

Treatment of a fresh leachate with high-strength organics and calcium from municipal solid waste (MSW) incineration plant by an up-flow anaerobic sludge blanket (UASB) reactor was investigated under mesophilic conditions, emphasizing the influence of organic loading rate (OLR). When the reactor was fed with the raw leachate (COD as high as 70,390-75,480 mg/L) at an OLR of 12.5 kg COD/(m³ d), up to ∼82.4% of COD was removed suggesting the feasibility of UASB process for treating fresh leachates from incineration plants. The ratio of volatile solids/total solids (VS/TS) of the anaerobic sludge in the UASB decreased significantly after a long-term operation due to the precipitation of calcium carbonate in the granules. Scanning electron microscopy (SEM) observation shows that Methanosaeta-like species were in abundance, accompanied by a variety of other species. The result was further confirmed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and sequencing.     

Effect of low power ultrasonic radiation on anaerobic biodegradability of sewage sludge

The effect of low power ultrasonic radiation on anaerobic biodegradability of sewage sludge was investigated. For this purpose, soluble substances and variation of microbial system of sewage sludge subjected to low power ultrasonic radiation were tested. The well known hydromechanical shear forces and heating effect of low frequency ultrasound plays a major role in the sludge pre treatment process. More, the increase of soluble substance may partly result from the destruction of microbial cell by excess ultrasonic pretreatment, which will inhibit the anaerobic process. By orthogonal tests, the optimal parameters were found to be an exposure time of 15 min, ultrasonic intensity of 0.35 W/cm² and ultrasonic power density of 0.25 W/ml. Under the optimal condition, anaerobic biodegradability of sewage sludge (R_(vss/ss) %) was increased by 67.6%. Consequently, it can be concluded that low power ultrasonic pretreatment is a valid method for improving anaerobic biodegradability of sewage sludge.     

Efficient,high-speed methane fermentation for sewage sludge using subcritical water hydrolysis as pretreatment

A novel biomass-energy process for the production of methane from sewage sludge using a subcritical water (sub-CW) hydrolysis reaction as pretreatment is proposed. The main substances of sewage sludge hydrolyzed by sub-CW at 513 K for 10 min were acetic acid, formic acid, pyroglutamic acid, alanine, and glycine. Fermentation experiments were conducted in an anaerobic-sludge reactor for two different samples: real sewage sludge and a model solution containing components typically produced by the sub-CW pretreatment of sewage sludge. In the experiment for the sub-CW pretreatment of sewage sludge, methane generation was twice that for non-pretreatment after 3 days of incubation. In the model experiment, the methane conversion was about 40% with the application of mixture of organic acids and amino acids after 5 days of incubation. Furthermore, the methane conversion was about 60% for 2 days when only organic acids, such as acetic acid and formic acid, were applied. Because acetic acid is the key intermediate and main precursor of the methanogenesis step, fermentation experiments were conducted in an anaerobic-sludge reactor with high concentrations of acetic acid (0.01–0.1 M). Nearly 100% of acetic acid was converted to methane and carbon dioxide in 1–3 days.     

Improvement strategy on enhanced biological phosphorus removal for municipal wastewater treatment plants: full-scale operating parameters, sludge activities, and microbial features

The poor quality of effluent discharged by municipal wastewater treatment plants (WWTPs) is threatening the safety of water ecology. This study, which integrated a field survey, batch tests, and microbial community identification, was designed to improve the effectiveness of the enhanced biological phosphorus removal (EBPR) process for WWTPs. Over two-thirds of the investigated WWTPs could not achieve total P in effluent lower than 0.5 mg/L, mainly due to the high ratio of chemical oxygen demand to P (28.6-196.2) in the influent. The rates of anaerobic P release and aerobic P uptake for the activated sludge varied from 0.22 to 7.9 mg/g VSS/h and 0.43 to 8.11 mg/g VSS/h, respectively. The fraction of Accumulibacter (PAOs: polyphosphate accumulating organisms) was 4.8 ± 2.0% of the total biomass, while Competibacter (GAOs: glycogen-accumulating organisms) accounted for 4.8 ± 6.4%. The anaerobic P-release rate was found to be an effective indicator of EBPR. Four classifications of the principal components were identified to improve the EBPR effluent quality and sludge activity.     

A comparison study on the high-rate co-digestion of sewage sludge and food waste using a temperature-phased anaerobic sequencing batch reactor system

Assessing contemporary anaerobic biotechnologies requires proofs on reliable performance in terms of renewable bioenergy recovery such as methane (CH₄) production rate, CH₄ yield while removing volatile solid (VS) effectively. This study, therefore, aims to evaluate temperature-phased anaerobic sequencing batch reactor (TPASBR) system that is a promising approach for the sustainable treatment of organic fraction of municipal solid wastes (OFMSW). TPASBR system is compared with a conventional system, mesophilic two-stage anaerobic sequencing batch reactor system, which differs in operating temperature of 1st-stage. Results demonstrate that TPASBR system can obtain 44% VS removal from co-substrate of sewage sludge and food waste while producing 1.2 m³CH₄/m³_system/d (0.2 m³CH₄/kgVS_added) at organic loading rate of 6.1 gVS/L/d through the synergy of sequencing-batch operation, co-digestion, and temperature-phasing. Consequently, the rapid and balanced anaerobic metabolism at thermophilic stage makes TPASBR system to afford high organic loading rate showing superior performance on OFMSW stabilization.     

Improved volatile fatty acids production from proteins of sewage sludge with anthraquinone-2,6-disulfonate (AQDS) under anaerobic condition

Organic matters in sewage sludge can be converted into volatile fatty acids (VFAs) as renewable carbon sources. This work for the first time applied anthraquinone-2,6-disulfonate (AQDS) for enhancing VFA production from sewage sludge. With 0.066 or 0.33 g AQDS g⁻¹ dried solids (DS), the yields for VFAs peak at 403 or 563 mg l⁻¹, 1.9- or 2.7-fold to the control. The accumulated VFAs were principally composed of acetate and propionate. The AQDS enhances degradation rates of model proteins (bovine serum albumin), but had little enhancement on that of model polysaccharides (dextrans). The acidification step is proposed the rate-limiting step for VFA production from sewage sludge, in which the AQDS molecules shuttle electrons to accelerate the redox reactions associated with amino acid degradation. Methanogenic activities are inhibited in the presence of AQDS. The AQDS-assisted VFAs are renewable organic carbon sources, although their direct use for anaerobic digestion is not advised.     

The Role of Particulate Organic Matter and Acetic Acid in the Removal of Phosphate in Anaerobic/Aerobic Activated Sludge Processes

Acetic acid is thought to be an important substrate for the removal of phosphate in anaerobic/aerobic activated sludge (AS) processes. However, the acetic acid content in municipal sewage is low, and the main organic compounds in such sewage are particulate organic matters (POM) that are converted to endogenous substrates (E(ntrapped) POM, i.e., EPOM) in AS processes. Thus, the question arises whether it is really acetate or POM, which is important for the removal of phosphate in full‐scale AS plants. AS was harvested from a full‐scale anaerobic/aerobic AS plant. The amount of phosphate released after the addition of acetic acid depends on the AS conditions, particularly the influent sewage quality. However, the amount of phosphate released by EPOM was not affected by the AS conditions, and the amount of phosphate released per AS concentration and per unit of time was calculated to be about 0.86 mg PO₄‐P/g MLSS/hour. When the AS concentration is 2.5 g/L and the mixed‐liquor retention time is 2 hours in the anaerobic zone, about 4 mg/L PO₄‐P is released from EPOM. Under these conditions, phosphate in such sewage is removed by full‐scale AS plants without using acetic acid. In the case of carbon deficiency, the introduction of primary sludge to the anaerobic zone promoted the release of phosphate.     

Nitrogen removal from wastewater with a low COD/N ratio at a low oxygen concentration

The goal of the study was to determine the effectiveness of nitrification and denitrification and the kinetics of ammonia removal from a mixture of wastewater and anaerobic sludge digester supernatant in an SBR at limited oxygen concentration. In addition, the COD removal efficiency and sludge production were assessed.In the SBR cycle alternating aerobic and anaerobic phases occurred; in the aeration phase the dissolved oxygen (DO) concentration was below 0.7 mg O₂/L. The low DO concentration did not inhibit ammonia oxidation-nitrification and the efficiency was ca. 96-98%. However, a relatively high COD concentration in the effluent was detected. The values of K_m and V_max, calculated from the Michaelis-Menten equation, were 43 mg N-NH₄/L and 15.64 mg N-NH₄/L h, respectively. Activated sludge production was almost stable (0.62-0.66 g MLVSS/g COD). A high net biomass production resulted from a low specific biomass decay rate of 0.0015 d⁻¹.     

Selection of optimum biological sludge for zinc removal from wastewater by a biosorption process

Summary Biosorption of zinc by sludge micro-organisms obtained from different steps of a conventional SWT plant has been studied. The best types of activated sludge for the process were found to be thickened, anaerobic and dewatered sludge giving up to 90–98% of metal elimination when working at initial zinc concentration lower than 50 mg/l. A relationship between pH and conditional stability constant has been found.     

Characteristics of hydrogen and methane production from cornstalks by an augmented two- or three-stage anaerobic fermentation process

This paper presents the co-production of hydrogen and methane from cornstalks by a two- or three-stage anaerobic fermentation process augmented with effective artificial microbial community. Two-stage fermentation by using the anaerobic sludge and DGGE analysis showed that effective and stable strains should be introduced into the system. We introduced Enterobacter aerogens or Clostridium paraputrificum into the hydrogen stage, and C. paraputrificum was proven to be more effective. In the three-stage process consisting of the improved hydrolysis, hydrogen and methane production stages, the highest soluble sugars (0.482 kg/kg cornstalks) were obtained after the introduction of Clostridium thermocellum in the hydrolysis stage, under the thermophilic (55 °C) and acidic (pH 5.0) conditions. Hydrolysates from 1 kg of cornstalks could produce 2.61 mol (63.7 l) hydrogen by augmentation with C. paraputrificum and 4.69 mol (114.6 l) methane by anaerobic granular sludge, corresponding to 54.1% energy recovery.     

Occurrence of Listeria sp and L monocytogenes in sewage sludge used for land application: effect of dewatering,liming and storage in tank on survival of Listeria species

The application of sewage sludge to agricultural land is widely used in France. To determine the impact of sludge treatments, concentrations of Listeria sp., Listeria monocytogenes and faecal indicators were monitored in five types of sludge from three sewage treatment plants in Angers (France) and its suburbs over a 1-year period. On the whole, bacteria were reduced in numbers through sludge treatments. Apart from liming, which leads to reduced levels of bacteria below detection limits, other sludge treatments did not eliminate Listeria sp. and faecal indicators. Listeria sp. and L. monocytogenes were found respectively in 87% and 73% of dewatered sludges and in 96% and 80% of sludges stored in tanks. Concentrations of L. monocytogenes, ranging from 0.15 to 20 MPN g(-1) dry matter in dewatered sludge and from 1 to 240 MPN g(-1) dry matter in sludge stored in tanks, did not show seasonal variations. Spreading of sanitised sludge onto agricultural land results in the addition of 10(6)-10(8) L. monocytogenes per hectare per year, which may contribute to the increase in the dissemination of this pathogenic species in the environment.     

The effect of Ni(II) on properties of bulking activated sludge and microbial analysis of sludge using 16S rDNA gene

This study investigated the effect of nickel on properties and microbial community of bulking activated sludge when 60-240 mg/L Ni(II) was dosed continuously in a sequencing batch reactor (SBR) over 350 days. Results showed that 120 mg/L nickel did not significantly inhibited removal of organic pollutant by activated sludge. However, the system was completely upset when 240 mg/L Ni(II) was dosed. Improvement of settling and dewatering ability was also observed with the addition of Ni(II). In addition, investigations by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) of 16S rDNA of bacteria strain demonstrated that Ni(II) significantly affected microbial community of bulking activated sludge, judging from the elimination of original species and emergence of possible new nickel-resistant bacteria. The effect of nickel on shift of microbial community was an important cause resulted in the improvement of sludge properties in this bulking activated sludge system.     

Mesophilic bio-liquefaction of lincomycin manufacturing biowaste: the influence of total solid content and inoculum to substrate ratio

As the potential source of environmental antibiotic pollution, large amount of biowaste generated from antibiotic fermentation manufacture highlights its beneficial utilization for resource and nutrients recovery; which is suitable for anaerobic bio-liquefaction (hydrolysis and acidification). However, its high solid content and residual antibiotics are a cause for concern. In this study, batch anaerobic experiments were conducted to evaluate the bio-liquefaction performance of lincomycin manufacturing biowaste at different total solid content (TS) and the ratios of seeding granular sludge (inoculum) to substrate (ISR). The results showed that lincomycin manufacturing biowaste had high bio-liquefaction efficiency, with the highest 10d volatile solid (VS) degradation rate being approximately 38%. The bio-liquefaction efficiency of protein could reach 100%. Predicted by response surface methodology, 1580 mg/L gVS volatile fatty acids (VFAs) and 497 mg/L gVS ammonium were obtained at a TS of 10%, ISR of 3 and solid retention time of 9.5 d, which is the optimum scenario.     

Laboratory-scale ultrasound pre-treated digestion of sludge: Heat and energy balance

The objective of this work was to maximize the digestibility of biological sludge to elucidate the feasibility of a new sludge management strategy to recover good quality sludge for agricultural use. The combined effects of organic loading rates (from 0.7 to 2.8 g VS L⁻¹ d⁻¹) and the degree of disintegration by anaerobic digestion of sonicated activated sludge were discussed, and the thermal and energetic balances were evaluated. Despite low sonication inputs, sludge digestion performance improved in terms of solids degradation and biogas production depending on the soluble organic load. The biogas production by sonicated sludge was higher (up to 30%) with respect to the control. Filterability improved during digestion of sonicated sludge at medium OLR due to a significant abatement of the fines. Thermal balances indicated that sonication may be a proper system to guarantee self-sustaining WAS mesophilic digestion. Nevertheless, thickening is a pre-requisite to achieve a positive energy balance.     

Methane recovery from the anaerobic codigestion of municipal sludge and FOG

The anaerobic biodegradability of a mix of municipal primary sludge (PS), thickened waste activated sludge (TWAS) and fat, oil, and grease (FOG) was assessed using semi-continuous feed, laboratory-scale anaerobic digesters operated at mesophilic (35 °C) and thermophilic (52 °C) temperature. Addition of a large FOG fraction (48% of the total VS load) to a PS + TWAS mix, resulted in 2.95 times larger methane yield, 152 vs. 449 mL methane @ STP/g VS added at 35 °C and 2.6 times larger methane yield, 197 vs. 512 mL methane @ STP/g VS added at 52 °C. The high FOG organic load fraction was not inhibitory to the process. The results of this study demonstrate the benefit of sludge and FOG codigestion.