Insight into performance of nitrogen removal enhanced by adding lactic acid-rich food waste fermentation liquid as carbon source in municipal wastewater treatment.

Lactic acid-rich fermentation liquid (LAFL) of food waste is found to act as a promising alternative carbon source for nitrogen removal in wastewater treatment. Here, LAFL was employed to investigate its impacts on nitrogen removal during raw municipal wastewater treatment with a comparison to sodium acetate (NaAc). Results indicated that nitrogen removals were comparable when incorporated with LAFL and NaAc (92.89 % v.s. 91.23 %). Unlike the utilization of NaAc, using LAFL could avoid suppressing the relative abundance of the nitrification genes and thus pose a negative risk to nitrogen removal during prolonged operation. The introduction of LAFL increased the stability and robustness of the functional microbial community and effectively reduced excess activated sludge (AS) generation by 109 % compared to NaAc addition, consequently enhancing nitrogen removal but diminishing the treatment cost. In general, LAFL exhibits prospective engineering application potentials and economic advantages in improving nitrogen removal by AS process.

Aeration pre-treatment role in improving the performance of bio-conditioning dewatering of food waste anaerobic digestate.

Bio-conditioning dewatering followed by activated sludge process (BDAS) is a promising technology for purifying food waste anaerobic digestate (FWAD). However, the bio-conditioning dewatering efficiency is often affected by FWAD properties and ambient temperature. Here, we firstly reported that aeration pre-treatment of FWAD played an important role in improving the bio-conditioning dewatering performance of FWAD. The study found that the accumulated carbonate (CO32-) in FWAD severely affected the flocculation of Fe-containing flocculant formed in microbial fermentation liquor due to the competitive consumption of the flocculant by CO32-. The capillary suction time (CST) and specific resistance to filtration (SRF) of the bio-conditioned FWAD increased from initial 77.8 s and 2.0 × 1012 m/kg to 122.7 s and 3.4 × 1012 m/kg, respectively, within 1 day of aeration. Prolonged aeration pre-treatment of FWAD could reduce its CO32- concentration and total alkalinity. Additionally, the aeration pre-treatment simultaneously decreased the proportion of macromolecular organic matter that hindered dewatering and the content of total solids (TS) and hydrophilic protein-like substances in FWAD. After 20 days of aeration followed by bio-conditioning, the CST and SRF reduced to final 36.5 s and 2.3 × 1011 m/kg, respectively, indicating a substantial improvement in dewatering performance. Successive forced aeration combined with the addition of CaCl2 to eliminate adverse factors mainly CO32- was a feasible and cost-effective strategy to realize bio-conditioning dewatering of FWAD in less than 2 days and a lower reagents dose of bio-conditioning, which was helpful in the engineering application of the novel BDAS process for FWAD purification.

A novel approach for purifying food waste anaerobic digestate through bio-conditioning dewatering followed by activated sludge process: A case study.

Although anaerobic digestion is the mainstream technology for treating food waste (FW), the high pollutant concentration in the resultant food waste anaerobic digestate (FWAD) often poses challenges for the subsequent biochemical treatment such as activated sludge process. In this study, taking a typical FW treatment plant as an example, we analyzed the reasons behind the difficulties in treating FWAD and tested a novel process called as bio-conditioning dewatering followed by activated sludge process (BDAS) to purify FWAD. Results showed that high concentrations of suspended solids (SS) (16439 ± 475 mg/L), chemical oxygen demand (COD) (24642 ± 1301 mg/L), and ammonium nitrogen (NH4+-N) (2641 ± 52 mg/L) were main factors affecting the purification efficiency of FWAD by the conventional activated sludge process. By implementing bio-conditioning dewatering for solid-liquid separation, near 100% of SS and total phosphorus (TP), 90% of COD, 38% of total nitrogen (TN), and 37% of NH4+-N in the digestate could be effectively removed or recovered, consequently generating the transparent filtrate with relatively low pollution load and dry sludge cake (<60% of moisture content). Furthermore, after ammonia stripping and biochemical treatment, the effluent met the relevant discharge standards regulated by China, with the concentrations of COD, TN, NH4+-N, and TP ranging from 151 to 405, 10-56, 0.9-31, and 0.4-0.8 mg/L, respectively. This proposed BDAS approach exhibited stable performance and low operating costs, offering a promising solution to purify FWAD in practical engineering and simultaneously realize resource recovery.

Feasibility of Bio-Coagulation Dewatering Followed by Bio-Oxidation Process for Treating Swine Wastewater.

The unsatisfactory performance of the conventional swine wastewater treatment is drawing increasing attention due to the large amount of refractory chemical oxygen demand (COD), nitrogen, and phosphorus attached to the suspended solids (SS). In this study, for the first time, a novel process based on bio-coagulation dewatering followed by a bio-oxidation (BDBO) system was developed to treat swine wastewater containing high-strength SS, COD, TN, and TP. Firstly, after the bio-coagulation process, the removal efficiencies of SS, COD, NH3-N, and TP reached as high as 99.94%, 98.09%, 61.19%, and 99.92%, respectively. Secondly, the filtrate of the bio-coagulation dewatering process was introduced into the subsequent bio-oxidation process, in which the residual COD and NH3-N were further biodegraded in a sequence batch reactor. In addition, the dewatering performance of the concentrated swine slurry was substantially improved, with the specific resistance to filtration decreasing from 17.0 × 1012 to 0.3 × 1012 m/kg. Moreover, the concentrated swine slurry was pressed and filtered into a semi-dry cake after pilot-scale bio-coagulation dewatering treatment. Finally, the concentrations of COD and NH3-N in the effluent after the BDBO process, ranging between 150-170 mg/L and 75-90 mg/L, met the relevant discharge standard. Compared to traditional treatments, the BDBO system has excellent large-scale potential for improving the treatment efficiency, shortening the operation period, and reducing the processing costs, and is emerging as a cost-effective alternative for the treatment of wastewater containing high concentrations of SS, COD, TN, and TP.

Enhancing propionic acid production in the acidogenic fermentation of food waste facilitated by a fungal mash under neutral pH.

Fungal mash derived from Aspergillus spp. is a green enzymatic additive for food waste (FW) valorization. In this study, the production of volatile fatty acids (VFAs) and the proportion of propionic acid (PA) in VFAs were increased by utilizing a complex enzyme (CE) obtained from Aspergillus oryzae. Results showed that CE addition significantly promoted SCOD concentration in the hydrolysis at a wide pH range from 4 to 9. In contrast, the production of VFAs was influenced by pH, and the highest yields of VFAs and PA were found at pH 7. At the CE dosage of 0.2 g/g VSS, the concentration of VFAs in the FW fermentation liquid reached 38.1 g COD/L with the PA proportion up to 42.7%, which increased by 107.9% and 63.7%, respectively, relative to that in the zero-dosage group. With CE continuing to be added, the C/N ratio declined, and the primary metabolic pathway was converted from acetic acid-type to PA-type. Further investigation of the dominant microbial communities and their metabolic capacities showed that the acrylate-mediated pathway was the potential metabolic reaction in PA-type fermentation. These results indicated that CE pretreatment was a feasible strategy to enhance the PA-rich fermentation of FW under neutral pH conditions.

Fungal mash enzymatic pretreatment combined with pH adjusting approach facilitates volatile fatty acids yield via a short-term anaerobic fermentation of food waste.

As an alternative for commercial enzyme, crude enzyme of fungal mash could promote food waste (FW) hydrolysis, but its specific effects coupled pH adjusting on the production of volatile fatty acids (VFAs) remains unknown. The crude enzyme produced from an Aspergillus awamori, named complex-amylase (CA), was added to short-term anaerobic system of FW fermentation. Results showed that adding CA significantly improved the solubility and degradability of biodegradable and non-biodegradable organics in FW, where the SCOD concentration with adding CA increased by 116.9% relative to the control but a marginal enhancement on VFAs yield. In contrast, adding CA combined with adjusting pH 8 markedly increased the VFAs production to 32.0 g COD/L, almost 10 times as much as the control. Besides, pH adjusting altered the metabolic pathway from lactate-type to butyrate-type. Adding CA coupled pH adjusting significant increase the component of butyrate compared with pH adjusting alone. Moreover, microbial community analysis indicated that adding CA reinforced proportion of the butyrate-producing bacteria (e.g., Dialister) under basic conditions, thus enhancing the butyrate metabolic pathways. This study demonstrated that fungal mash pretreatment coupled pH conditioning could be an economical way to enhance VFAs yield for FW valorization during anaerobic fermentation.

Occurrence of bacterial and viral fecal markers in municipal sewage sludge and their removal during sludge conditioning processes.

Fecal contamination in wastewater treatment system may pose severe threats to human health, but the detailed contamination of fecal bacterial and viral pathogens in municipal sewage sludge remains unclear. In addition, it is also unclear how sludge conditioning treatments would impact the distribution of fecal markers in conditioned sewage sludge. Before addressing these two issues, the possible polymerase chain reaction (PCR) inhibition effect when determining the abundances of fecal markers in both sludge solids and sludge supernatants should be solved, and methods of effectively concentrating fecal markers from sludge supernatant should also be developed. In the present study, we found that the serial tenfold dilution effectively reduced the PCR inhibition effect when determining the abundances of fecal markers including cross-assembly phages (CrAssphage), JC polyomavirus (JCPyV), human-specific HF183 bacteroides (HF183), human BK polyomavirus (BKPyV), human adenovirus (HAdV) and Escherichia coli (EC), while the utilization of negatively charged HA membrane was effective to recover fecal markers from sludge supernatant. The results of a six-month monitoring revealed that gene markers of CrAssphage, JCPyV, HF183, BKPyV, HAdV, and EC can be detected in municipal sewage sludge collected from a local wastewater treatment plant. Among the investigated four chemical conditioning methods, i.e., chemical conditioning with polyacrylamide (PAM), Fe[III]/CaO, or Fenton's reagent, and chemical acidification conditioning, chemical conditioning with Fenton's reagent was much more effective than the other three conditioning methods to reduce the abundances of fecal markers in the supernatant and solid of conditioned sewage sludge. Furthermore, the investigated fecal markers in the conditioned sewage sludge can be simultaneously attenuated by employing suitable conditioning methods, consequently reducing the associated environmental risks.

Food waste hydrolysate as a carbon source to improve nitrogen removal performance of high ammonium and high salt wastewater in a sequencing batch reactor.

The high ammonium and high salt (HAHS) wastewater generated from the anaerobic digestate of food waste is usually difficult to be treated by biological process because of its low C/N ratio. Herein, food waste hydrolysate (FWH) is rich in readily biodegradable organic matter, was utilized as carbon source to enhance the nitrogen removal of HAHS in the activated-sludge system. Results showed that compared with the control average total nitrogen removal efficiency increased from 73.4% to 94.9% and effluent declined from 281.4 mg/L to 53.9 mg/L by adding FWH at the C/N ratio of 6, satisfying the sewage discharge standard regulated by China. Besides, FWH utilization led to higher selectivity of the species responsible for nitrogen removal in related to glucose-adding group, which were dominated by Flavobacteriaceae, Melioribacteraceae, PHOS-HE36, and Rhodobacteraceae after a long-term operation. In general, FWH is an alternative carbon source to enhance nitrogen removal in HAHS wastewater treatment.

Efficient utilization of the electron energy of antibiotics to accelerate Fe(III)/Fe(II) cycle in heterogeneous Fenton reaction induced by bamboo biochar/schwertmannite.

The discharge of antibiotics evokes environmental health crisis, and is also a waste of organic energy. Currently, heterogeneous Fenton for antibiotics removal has attracted growing attentions due to wide pH range and no iron sludge production, however, it often suffers from a low formation rate of Fe(II), resulting in difficult application of heterogeneous Fenton technology in sewage treatment. To overcome this drawback, bamboo biochar (BB) is coupled with schwertmannite (Sch) through Acidithiobacillus ferrooxidans-mediated Fe(II) oxidation reaction to obtain a heterogeneous catalyst (Sch/BB) with high adsorption performance and Fenton activity. According to the analysis of experimental results, electrons around C (from BB) can easily transfer to Fe by Fe-O-C bonds to expedite ≡Fe(III)/≡Fe(II) cycle, while electrons of antibiotics adsorbed on Sch/BB surface are effectively utilized to maintain the efficient regeneration of ≡Fe(II) through BB electron shuttle or Fe-O-C bonds between Sch/BB and pollutants, further causing a superior Fenton activity (98% antibiotics removal) of Sch/BB. Moreover, due to its excellent adsorption performance, Sch/BB as filter materials can effectively remove dye pollutants in flow wastewater. These findings provided a high-activity and practical heterogeneous Fenton catalyst for pollutants degradation, while a new perspective for efficient utilization of the electrons of organic pollutants was given.

Nitrogen removal performance of high ammonium and high salt wastewater by adding carbon source from food waste fermentation with different acidogenic metabolic pathways.

Food waste fermentation liquid components, mainly lactate and volatile fatty acids (VFAs), can be used as alternative carbon sources to improve the nitrogen removal efficiency. To investigate the effects of carbon sources generated from food waste (FW) fermentation liquid on nitrogen removal for the treatment of high ammonium and high salt wastewater (HAHS), the lactate, acetate, propionate, butyrate, and their mixtures were added in activated sludge systems operating over 130-days. Lactate and butyrate inhibited nitrifiers by enriching polyphosphate accumulating organisms (PAOs), thus deteriorated nitrogen removal after a long-term period. When fed with acetate or propionate, the dominant glycogen accumulating organisms (GAOs) groups simultaneously realized nitrification and denitrification. The mixed carbon source enhanced microbial community robustness and the transformation of Polyhydroxyalkanoate (PHA), advancing nitrogen removal efficiency. Mixed carbon source of acetate-propionate was preferred, in which the coexisting groups of GAOs and PAOs enhanced the denitrification rate of denitrifiers and kept balancing with nitrifiers, where the highest denitrification rate (DNR) was 1.05 mg N/(h·g VSS) and the average TN removal efficiency was above 98% under the maximum nitrogen load of 0.48 kg N/(kg VSS·d). In addition, the primary pathways of nitrogen removal were heterotrophic nitrification and denitrification, since the autotrophic nitrifiers were inhibited by the free ammonium and salinity. This study illustrated the differences of nitrogen removal performance and mechanisms with fermentation liquid components as carbon sources processing of HAHS wastewater.

Biosynthesized Schwertmannite@Biochar composite as a heterogeneous Fenton-like catalyst for the degradation of sulfanilamide antibiotics.

Schwertmannite was successfully loaded onto biochar (Sch@BC) using a biosynthetic method. The physicochemical properties and structural morphology of Sch@BC were explored using XRD, SEM, BET, and XPS. The results showed that introducing biochar can effectively prevent the agglomeration of Sch. The catalytic activity of Sch@BC in the Fenton-like degradation of sulfamethoxazole (SMX) was also systematically investigated under different reaction conditions. Under optimum conditions ([SMX] = 10 mg L-1, [H2O2] = 2.0 mM, Sch@BC = 1.0 g L-1 and initial pH = 3.0), the removal efficiencies of the SMX and total organic carbon (TOC) were 100% and 45.9%, respectively, within 60 min of the reaction. The results of the radical scavenger effect and ESR studies suggested that the SMX degradation in the Sch@BC/H2O2 system was dominated by a heterogeneous Fenton-like reaction. The repeated use of Sch@BC for SMX degradation demonstrated its reusability and stability in Fenton-like reactions. There was also speculation about the degradation mechanism and pathways of SMX. Furthermore, under the same conditions, the removal efficiencies of sulfadiazine (SD) and sulfisoxazole (SIZ) under Fenton-like degradation in the Sch@BC system were 91% and 93%. The results provide a theoretical basis and practical guidance for the creation of a new catalyst using biochar as a support material for the degradation of sulfanilamide antibiotics.

Synthesis and assessment of schwertmannite/few-layer graphene composite for the degradation of sulfamethazine in heterogeneous Fenton-like reaction.

Schwertmannite (sch), an iron oxyhydrosulfate mineral, can catalyse a Fenton-like reaction to degrade organic contaminants, but the reduction of Fe(III) to Fe(II) on the surface of schwertmannite is a limiting step for the Fenton-like process. In the present study, the sch/few-layer graphene (sch-FLG) composite was synthesized to promote the catalytic activity of sch in a Fenton-like reaction. It was found that sch can be successfully carried by FLG in sch-FLG composite, mainly via the chemical bond of Fe-O-C on the surface of sch-FLG. The sch-FLG exhibited a much higher catalytic activity than sch or FLG for the degradation of sulfamethazine (SMT) in the heterogeneous Fenton-like reaction, which resulted from the fact that the FLG can pass electrons efficiently. The degradation efficiency of SMT was around 100% under the reaction conditions of H2O2 200-500 mg l-1, sch-FLG dosage 1-2 g l-1, temperature 28-38°C, and initial solution pH 1-9. During the repeated uses of sch-FLG in the Fenton-like reaction, it maintained a certain catalytic activity for the degradation of SMT and the mineral structure was not changed. In addition, SMT may be finally mineralized in the Fenton-like reaction catalysed by sch-FLG, and the possible degradation pathways were proposed. Therefore, the sch-FLG is an excellent catalyst for SMT degradation in a heterogeneous Fenton-like reaction.

Importance of sludge conditioning in attenuating antibiotic resistance: Removal of antibiotic resistance genes by bioleaching and chemical conditioning with Fe[III]/CaO.

Conditioning can drastically improve the dewaterability of sewage sludge and thus it is widely practiced in most wastewater treatment plants (WWTPs). In WWTPs, various antibiotic resistance genes (ARGs) present in sewage are concentrated in the sewage sludge, but the effect of sludge conditioning on ARGs in sewage sludge remains unclear. Here, we evaluated and compared the effectiveness of four sludge conditioning methods (namely chemical conditioning with polyacrylamide (PAM), chemical conditioning with Fe[III]/CaO, bioleaching conditioning, and chemical acidification conditioning) and an aerobic incubation control in removing 46 target ARGs and intI1 from a municipal sewage sludge. The damage of sludge microbial cells and the change in the sludge bacterial community during the various sludge conditioning treatments were also characterized. The results suggested that the chemical conditioning with PAM and aerobic incubation treatment did not remove ARGs and intI1 from the sewage sludge. The chemical acidification reduced the absolute abundances of most ARGs and intI1, but increased their relative abundances. However, the chemical conditioning with Fe[III]/CaO and bioleaching conditioning reduced both the absolute and relative abundances of most ARGs and removed a majority of extracellular ARGs in the sludge. During sludge conditioning treatments, the sludge microbial cells were severely damaged to decrease the total bacterial biomass in sludge, and accordingly the bacterial hosts carrying ARGs and intI were effectively damaged to reduce the absolute abundances of most ARGs and intI1. In addition, the sludge bacterial community in conditioned sludge determined the relative abundances of residual ARGs. Our findings suggest that sludge conditioning can be an important sludge treatment process in attenuating antibiotic resistance in sewage sludge, and bioleaching and chemical conditioning with Fe[III]/CaO can be employed as effective conditioning ways to reduce ARGs in sewage sludge, potentially limiting their release to the environment.

[Effect of acidification on the dewaterability of sewage sludge in bioleaching].

Batch experiments were performed to exploit the effect and the mechanism of bioleaching on sludge dewaterability by the inoculation of Acidithiobacillus ferrooxidans LX5 in this study. Besides, chemical leaching experiments using sulphuric acid were also performed as control to study the effect of acidification on sludge dewaterability. During the processes of both biological and chemical leaching, Zeta potential, cell lyses, morphology and structure of sludge flocs were monitored. Results showed that along with the acid production and hence the decrease of pH during bioleaching, the specific resistance of bioleached sludge decreased systematically from 1.81 x 10(12) m x kg(-1) to 0.59 x 10(12) m x kg(-1), whilst Zeta potential increased from -25.2 mV to 9.6 mV, and the natural sedimentation rate increased to as high as 48% at pH 2.90. In chemical leaching, the specific resistance decreased continuously to a minimum value of 2.6 x 10(12) m x kg(-1) at pH 3.35 and then started to increase. Zeta potential increased with the decrease of pH, and reached zero at pH 2.90. At strong acid condition, sludge cells could be decomposed, resulting in the increase of total dissolved phosphorus in centrifugal liquor of chemical leached sludge. However, this phenomenon was not observed in bioleaching process because that the phosphorus was utilized by the abundant microorganism in system. Observation by SEM showed that there was no obvious change in the flocs structure of both sludge at pH 3.35 except for that some secondary minerals appeared only in bioleached sludge. These results revealed that decrease of absolute value of Zeta potential and formation of secondary minerals caused by bioleaching were responsible for the improvement of sludge dewaterability.

Improvement of sludge dewaterability and removal of sludge-borne metals by bioleaching at optimum pH.

Bio-acidification caused by bio-oxidation of energy substances during bioleaching is widely known to play an important role in improving sludge-borne metals removal. Here we report that bioleaching also drastically enhances sludge dewaterability in a suitable pH level. To obtain the optimum initial concentrations of energy substances and pH values for sludge dewaterability during bioleaching, bio-oxidation of Fe(2+) and S(0) under co-inoculation with Acidithiobacillus thiooxidans TS6 and Acidothiobacillus ferrooxidans LX5 and their effects on sludge dewaterability and metals removal during sludge bioleaching were investigated. Results indicated that the dosage of energy substances with 2g/L S(0) and 2g/L Fe(2+) could obtain bio-oxidation efficiencies of up to 100% for Fe(2+) and 50% for S(0) and were the optimal dosages for sludge bioleaching. The removal efficiencies of sludge-borne Cu and Cr could reach above 85% and 40%, respectively, and capillary suction time (CST) of bioleached sludge decreased to as low as ∼10s from initial 48.9s for fresh sludge when sludge pH declined to ∼2.4 through bioleaching. These results confirm the potential of bioleaching as a novel method for improving sludge dewaterability as well as removal of metals.

[Effect of different sludge retention time (SRT) on municipal sewage sludge bioleaching continuous plug flow reaction system].

A plug-flow bio-reactor of 700 L working volume for sludge bioleaching was used in this study. The reactor was divided into six sections along the direction of the sludge movement. Fourteen days of continuous operation of sludge bioleaching with different sludge retention time (SRT) under the condition of 1.2 m3 x h(-1) aeration amount and 4 g x L(-1) of microbial nutritional substance was conducted. During sludge bioleaching, the dynamic changes of pH, DO, dewaterability (specific resistance to filtration, SRF) of sewage sludge in different sections were investigated in the present study. The results showed that sludge pH were maintained at 5.00, 3.00, 2.90, 2.70, 2.60 and 2.40 from section 1 to section 6 and the SRF of sludge was drastically decreased from initial 0.64 x 10(13) m x kg(-1) to the final 0.33 x 10(13) m x kg(-1) when bioleaching system reached stable at hour 72 with SRT 2.5d. In addition, the sludge pH were maintained at 5.10, 4.10, 3.20, 2.90, 2.70 and 2.60, the DO value were 0.43, 1.47, 3.29, 4.76, 5.75 and 5.88 mg x L(-1) from section 1 to section 6, and the SRF of sludge was drastically decreased from initial 0.56 x 10(13) to the final 0.20 x 10(13) m x kg(-1) when bioleaching system reached stable at hour 120 with SRT 2 d. The pH value was increased to 3.00 at section 6 at hour 48 h with SRT 1.25 d. The bioleaching system imbalanced in this operation conditions because of the utilization efficiency of microbial nutritional substance by Acidibacillus spp. was decreased. The longer sludge retention time, the easier bioleaching system reached stable. 2 d could be used as the optimum sludge retention time in engineering application. The bioleached sludge was collected and dewatered by plate-and-frame filter press to the moisture content of dewatered sludge cake under 60%. This study would provide the necessary data to the engineering application on municipal sewage sludge bioleaching.

Isolation and characterization of a nitrobenzene-degrading bacterium Klebsiella ornithinolytica NB1 from aerobic granular sludge.

Strain NB1 was isolated from aerobic granular sludge capable of degrading nitrobenzene. Effects of several factors including pH, temperature, salinity, and second carbon/nitrogen source as co-substrate on the biodegradation of nitrobenzene by strain NB1 were investigated. Results showed that the optimal conditions for the biodegradation of nitrobenzene by strain NB1 were at pH 7.0 and 28-35°C. Under these conditions, the biodegradation rate of nitrobenzene could reach 9.29mgl(-1)h(-1) when the initial nitrobenzene concentration was 600mgl(-1). The addition of 1840mgl(-1) glucose or 500mgl(-1) ammonium chloride could slightly enhance the biodegradation efficiency, but even more addition of glucose or ammonium chloride delayed the biodegradation. Strain NB1 could degrade nitrobenzene in the presence of less than 3% NaCl (w/v %). Based on morphological and physiological characteristics as well as the phylogenetic analysis of 16S rDNA sequences, strain NB1 was identified as Klebsiella ornithinolytica.

Enhancing sewage sludge dewaterability by bioleaching approach with comparison to other physical and chemical conditioning methods.

The sewage sludge conditioning process is critical to improve the sludge dewaterability prior to mechanical dewatering. Traditionally, sludge is conditioned by physical or chemical approaches, mostly with the addition of inorganic or organic chemicals. Here we report that bioleaching, an efficient and economical microbial method for the removal of sludge-borne heavy metals, also plays a significant role in enhancing sludge dewaterability. The effects of bioleaching and physical or chemical approaches on sludge dewaterability were compared. The conditioning result of bioleaching by Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans on sludge dewatering was investigated and compared with the effects of hydrothermal (121 degrees C for 2 hr), microwave (1050 W for 50 sec), ultrasonic (250 W for 2 min), and chemical conditioning (24% ferric chloride and 68% calcium oxide; dry basis). The results show that the specific resistance to filtration (SRF) or capillary suction time (CST) of sludge is decreased by 93.1% or 74.1%, respectively, after fresh sludge is conditioned by bioleaching, which is similar to chemical conditioning treatment with ferric chloride and calcium oxide but much more effective than other conditioning approaches including hydrothermal, microwave, and ultrasonic conditioning. Furthermore, after sludge dewatering, bioleached sludge filtrate contains the lowest concentrations of chroma (18 times), COD (542 mg/L), total N (TN, 300 mg/L), NH4(+)-N (208 mg/L), and total P (TP, 2 mg/L) while the hydrothermal process resulted in the highest concentration of chroma (660 times), COD (18,155 mg/L), TN (472 mg/L), NH4(+)-N (381 mg/L), and TP (191 mg/L) among these selected conditioning methods. Moreover, unlike chemical conditioning, sludge bioleaching does not result in a significant reduction of organic matter, TN, and TP in the resulting dewatered sludge cake. Therefore, considering sludge dewaterability and the chemical properties of sludge filtrate and resulting dewatered sludge cakes, bioleaching has potential as an approach for improving sludge dewaterability and reducing the cost of subsequent reutilization or disposal of dewatered sludge.

[Improvement of municipal sewage sludge dewaterability by bioleaching: a pilot-scale study with sequence batch reaction model].

To observe the bioleaching effect on sewage sludge dewaterability, three consecutive batch bioleaching experiments were conducted through a bioleaching bio-reactor with 700 L of working volume. Subsequently, the bioleached sludge was dewatered by using chamber filter press. The results show that the 1st batch bioleaching process can be finished within 90 hours if the aeration amount was 1.2 m3/h with the 1: 15 mixing ratio of bioleached sludge to raw sludge. The pH of sludge declines from initial 6.11 to 2.33 while ORP increased from initial -134 mV to finial 507 mV. The specific resistance to filtration (SRF) of the tested sludge was decreased from original 1.00 x 10(13) m/kg to final 0.09 x 10(13) m/kg after bioleaching. For the subsequent two batch trials, the bioleaching process can be finished in 40 hours and 46 hours, respectively. Likewise, sludge SRF is also significantly decreased to 0.19 x 10(13) m/kg and 0.36 x 10(13) m/kg if the mixing ratio of bioleached sludge to fresh sludge is 1:1 although the microbial nutrient substance dosage is reduced by 25% and 50% for 2nd, and 3rd batch experiments, respectively. The harvested bioleached sludge from three batch trails is dewatered by chamber filter press with 0.3-0.4 MPa working pressure for 2 hours. It is found that the moisture of dewatered sludge cake can be reduced to 58%, and that the dewatered sludge cake is of khaki appearance and didn't emit any offensive odor. In addition, it is also observes that sludge organic matter only changed a bit from 52.9% to 48.0%, but 58% of sludge-borne Cu and 88% of sludge-borne Zn can be removed from sludge by bioleaching process. Therefore, dual goals for sludge-borne heavy metal removal and sludge dewatering of high efficiency can be achieved simultaneously through the approach mentioned above. Therefore, bioleaching technique is of great engineering application for the treatment of sewage sludge.

[Influence of bioleaching on dewaterability of cattle biogas slurry].

The dewaterability of cattle biogas slurry facilitated by bioleaching was investigated through batch experiments with co-inoculation of different Acidophilic thiobacilli (Acidithiobacillus thiooxidans TS6 or Acidithiobacillus ferrooxidans LX5). The experiment was set the following 5 treatments: (1) original biogas slurry (CK), (2) 4 g x L(-1) Fe(2+) (uninoculation), (3)2 g x L(-1) S(0) + 25 mL A. t, (4) 4 g x L(-1) Fe(2+) + 25 mL A. f and (5) 2 g x L(-1) S(0) + 4 g x L(-1) Fe(2+) + 12.5 mL A. t + 12.5 mL A. f. During bioleaching, dynamic changes of pH, ORP, Fe(2+), F(3+), total Fe, the settleability, the turbidity of the supernatant after settling for 12 h, and the dewaterability (expressed as specific resistance to filtration gamma or capillary suction time, CST) of biogas slurry were monitored. Results show that specific resistance gamma and CST of bioleached biogas slurry are reduced drastically for the treatments of original biogas slurry spiked with only Fe(2+), the treatment of original biogas slurry co-spiked with Fe(2+) and Acidithiobacillus ferrooxidans LX5, and the treatment of original biogas slurry co-spiked with Fe(2+), S(0) and two Acidophilic thiobacilli. Taking the dewaterability, settleability, the turbidity of the supernatant fluid after settle 12 h and economical cost into account, the treatment of original biogas slurry co-spiked with Fe(2+) and Acidithiobacillus ferrooxidans LX5 is the most suitable pattern for cattle biogas slurry bioleaching. After bioleaching, 1.14% of organic matter, 0.09% of N, 0.05% of P, and 0.1% of K are lost in the bioleaching process, but it don't affect its fertilizer efficiency. Meanwhile, the 63.2% of Cu and 91.3% of Zn are removed from the biogas slurry, and elimination efficiencies of total coliforms in bioleached slurry exceed 99%. This study might provide a new approach for treatment and disposal of biogas slurry.