Soluble Chemical Oxygen Demand Research Articles

Pilot-scale two-phase anaerobic digestion of deoiled food waste and waste activated sludge: Effects of mixing ratios and functional analysis

Anaerobic co-digestion of deoiled food waste (dFW) and waste activated sludge (WAS) can address the challenges derived from mono-digestion of FW. In the present study, a pilot-scale methanogenic bioreactor of a two-phase anaerobic digestion system was developed to explore the impact of dFW/WAS volatile solids ratios on the overall performance, microbial community, and metabolic pathways. Besides, the tech-economic of the system was analyzed. The results showed that the degradation efficiency of soluble chemical oxygen demand (SCOD) was more than 84.90% for all the dFW/WAS ratios (v/v) (1:0, 39:1, 29:1, 19:1 and 9:1). Moreover, the dominant genus of bacteria and archaea with different ratios were Lactobacillus (66.84–98.44%) and Methanosaeta (53.66–80.09%), respectively. Co-digestion of dFW and WAS (29: 1 in v/v ratios) obtained the highest yield of methane (0.41 L CH4/Ladded) with approximately 90% of SCOD being removed. In the pilot-scale experiment, the co-digestion of FW and WAS makes positive contribution to reusing solid waste for improving solid management.

Molecular insights into the dissolved organic matter of leather wastewater in leather industrial park wastewater treatment plant

Leather wastewater (LW) effluent is characterized by complex organic matter, high salinity, and poor biodegradability. To meet the discharge standards, LW effluent is often mixed with municipal wastewater (MW) before being treated at a leather industrial park wastewater treatment plant (LIPWWTP). However, whether this method efficiently removes the dissolved organic matter (DOM) from LW effluent (LWDOM) remains debatable. In this study, the transformation of DOM during full-scale treatment was revealed using spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry. LWDOM exhibited higher aromaticity and lower molecular weight than DOM in MW (MWDOM). The DOM properties in mixed wastewater (MixW) were similar to those in LWDOM and MWDOM. The MixW was treated using a flocculation/primary sedimentation tank (FL1/PST), anoxic/oxic (A/O) process, secondary sedimentation tank (SST), flocculation/sedimentation tank, denitrification filter (FL2/ST-DNF), and an ozonation contact reactor (O3). The FL1/PST unit preferentially removed the peptide-like compounds. The A/O-SST units had the highest removal efficiencies for dissolved organic carbon (DOC) (61.34 %) and soluble chemical oxygen demand (SCOD) (52.2 %). The FL2/ST-DNF treatment removed the lignin-like compounds. The final treatment showed poor DOM mineralization efficiency. The correlation between water quality indices, spectral indices, and molecular-level parameters indicated that lignin-like compounds were strongly correlated with spectral indices and CHOS compounds considerably contributed to the SCOD and DOC. Although the effluent SCOD met the discharge standard, some refractory DOM from LW remained in the effluent. This study illustrates the composition and transformation of DOM and provides theoretical guidance for improving the current treatment processes.

Anaerobic Digestion of Olive Mill Wastewater in the Presence of Biochar

Biological treatments focused on stabilizing and detoxifying olive mill wastewater facilitate agronomic reuse for irrigation and fertilization. Anaerobic digestion is particularly attractive in view of energy recovery, but is severely hampered by the microbial toxicity of olive mill wastewater. In this work, the addition of biochar to the digestion mixture was studied to improve the stability and efficiency of the anaerobic process. Kinetics and yields of biogas production were evaluated in batch digestion tests with biochar concentrations ranging from 0 to 45 g L−1. The addition of biochar reduced sensibly the lag phase for methanogenesis and increased the maximum rate of biogas generation. Final yields of hydrogen and methane were not affected. Upon addition of biochar, soluble COD removal increased from 66% up to 84%, and phenolics removal increased from 50% up to 95%. Digestate phytotoxicity, as measured by seed germination tests, was reduced compared to raw wastewater. Addition of biochar further reduced phytotoxicity and, furthermore, a stimulatory effect was observed for a twenty-fold dilution. In conclusion, biochar addition enhances the anaerobic digestion of olive mill wastewaters by effectively reducing methanogenesis inhibition and digestate phytotoxicity, thus improving energy and biomass recovery.

Treatment of citrus juice process wastewater with UASB and biogas production

A lab-scale up-flow anaerobic sludge blanket (UASB) reactor was used for biogas production from the citrus juice process wastewater (CPWW). The volume of the reactor was 11.5 L. During 200 days of the reactor, the organic loading rate (OLR) value changed from 1.8-21.9 kgCOD./m3.d, upflow velocities (Vup) 0.1-5.2 m/h and hydraulic retention time (HRT) changed from 0.042 to 4.16 days. The reactor showed a stable performance at all organic loadings. Experimental chemical oxygen demand (COD) removal efficiencies were 71.5 ± 21% and 83.3 ± 16.3% for total COD (TCOD) and soluble COD (SCOD), respectively. The acetic acid concentration changed from 135 to 650 mg/L. The temperature was kept in the range of 35.1 ± 1.4 oC, the pH in the range of 6.6 ± 0.2, and the alkalinity was controlled daily and kept in the range of 411 ± 273 CaCO3 mg/L. After anaerobic reactions, 6283 ± 3476 m3/d biogas was produced and the methane concentration in the biogas was 65.5 ± 11.5%. Depending on the methane production, the annual energy value potential that can be obtained from the existing UASB reactor is estimated as 48,768 kWh.

Improvement of Asterarcys quadricellulare biomass solubilization and subsequent biogas production via pretreatment approaches: structural changes and kinetic modeling evaluation.

This study investigated the effect of enzymatic and hydrothermal pretreatment approaches on the solubilization of organic matter, structure, and biogas yield from microalgal biomass. The soluble chemical oxygen demand (sCOD) concentration increased by 1.21-3.30- and 5.54-6.60-fold compared to control by enzymatic and hydrothermal pretreatments respectively. The hydrothermal pretreatment affected the structural changes in the microalgal biomass markedly; nonetheless, increased enzymatic concentration also had a definite effect on it as determined by qualitative approaches like scanning electron microscopy and Fourier transform infrared spectroscopy. Also, the hydrothermal pretreatment (100°C for 30min) resulted in the highest biogas production potential (P) of 765.37 mLg-1 VS at a maximum biogas production rate (Rm) of 22.66 mLg-1day-1 with a very short lag phase (λ) of 0.07days. The biogas production of pretreated microalgal biomass particularly at higher enzyme dose (20%, 24h) and higher hydrothermal pretreatment temperature (120°C, 30min) showed a significant but weak correlation (R = 0.53) with sCOD, thus demonstrating that the less organic matter was used up for the biogas production. The modified Gompertz model explained the anaerobic digestion of microalgal biomass more accurately and had a better fit to the experimental data comparatively because of the low root mean square error (3.259-16.728), residual sum of squares (78.887-177.025), and Akaike's Information Criterion (38.605-62.853).

Optimization of Operating Parameters for Two-Phase Anaerobic Digestion Treating Slaughterhouse Wastewater for Biogas Production: Focus on Hydrolytic–Acidogenic Phase

In a two-phase anaerobic digestion process, enhanced biogas production and organic pollutant removal depend on the stability and performance of the hydrolytic–acidogenic and methanogenic phases. Additionally, the hydrolytic–acidogenic phase is a rate-limiting step, which calls for the further optimization of operating parameters. The objective of this study was to optimize the operating parameters of the hydrolytic–acidogenic reactor (HR) in the two-phase anaerobic digestion treating slaughterhouse wastewater. The experiment was carried using bench-scale sequential bioreactors. The hydrolytic–acidogenic reactor operating parameters were optimized for six different hydraulic retention times (HRTs) (6–1 day) and organic loading rates (OLRs) (894.41 ± 32.56–5366.43 ± 83.80 mg COD/L*day). The degree of hydrolysis and acidification were mainly influenced by lower HRT (higher OLR), and the highest values of hydrolysis and acidification were 63.92% and 53.26% at an HRT of 3 days, respectively. The findings indicated that, at steady state, the concentrations of soluble chemical oxygen demand (SCOD) and total volatile fatty acids (TVFAs) decrease as HRT decreases and OLR increases from HRTs of 3 to 1 day and 894.41–1788.81 mg COD/L*day, respectively, and increase as the HRT decreases from 6 to 4 days. The concentration of NH4+-N ranges from 278.67 to 369.46 mg/L, which is not in the range that disturbs the performance and stability of the hydrolytic acidogenic reactor. It was concluded that an HRT of 3 days and an ORL of 1788.81 mg COD/L*day were selected as optimal operating conditions for the high performance and stability of the two-phase anaerobic digestion of slaughterhouse wastewater in the hydrolytic–acidogenic reactor at a mesophilic temperature. The findings of this study can be applicable for other agro-process industry wastewater types with similar characteristics and biowaste for value addition and sustainable biowaste management and safe discharge.

Development of an Integrated Biorefinery System for Bioconversion of Lignocellulosic Biomass to Polyhydroxyalkanoates and Biohydrogen

A sustainable lignocellulosic biomass-based biorefinery requires complete utilization and valorization of the biomass components. In the present study, a phase-separated pretreatment (chemo mechanical─delignification followed by bacterial pretreatment) was performed to fractionate lignin and cellulose-rich residue from rice straw biomass (RSB) to utilize lignin for polyhydroxyalkanoates (PHA) and cellulose-rich residue for biohydrogen production. A higher lignin removal of 81.4% was obtained through combined H2O2–homogenizer pretreatment. The lignin was utilized as a substrate by Bacillus cereus for PHA production. The cellulose-rich delignified RSB was hydrolyzed with cellulase-secreting bacteria. A higher chemical oxygen demand solubilization of 38.2% was achieved in delignified and bacterially (Delig-Bac) pretreated RSB than bacterially pretreated (Bac) alone (22.9%) and control (3.43%). A higher cellulose solubilization of 35.8% was obtained in Delig-Bac pretreated RSB than Bac alone (21.5%). A higher PHA concentration, content, and yield of 480 mg/L, 56%, and 561 mg/g were obtained from 2.970 g/L of lignin. Higher biohydrogen production of 66 mL/gVS was achieved in Delig-Bac pretreated RSB. The economic analysis revealed that Delig-Bac was found to be economically feasible with a net profit of 4.18 USD/m3 when compared to Bac (−457.4 USD/m3).

Combined sodium citrate and ultrasonic pretreatment of waste activated sludge for cost effective production of biogas

This study aimed to pretreat the waste activated sludge (WAS) by ultrasonication in an energy efficient way by combining sodium citrate with ultrasonic pretreatment at 0.03 g/g suspended solids (SS) of dosage. The ultrasonic pretreatment was done at various (20–200 W) power levels, sludge concentration (7 to 30 g/L), sodium citrate dosages (0.01 to 0.2 g/g SS). An elevated COD solubilization of 26.07 ± 0.6 % was achieved by combined pretreatment at a treatment time of 10 min, ultrasonic power level of 160 W when compared to individual ultrasonic pretreatment (18.6 ± 0.5 %). A higher biomethane yield of 0.26 ± 0.009 L/g COD was achieved in sodium citrate combined ultrasonic pretreatment (SCUP) than ultrasonic pretreatment (UP) 0.145 ± 0.006 L/g COD. Almost 50% of the energy can be saved through SCUP when compared to UP. Future study evaluating SCUP in continuous mode anaerobic digestion is vital.

Evaluation of biogas production and pollutant removal efficiency of two-phase anaerobic digestion treating slaughterhouse effluent

Treatment of slaughterhouse and other agro-processing industry effluent has become important due to continuous global population growth and meat demand, particularly in developing countries, for sustainable biowaste management as well as value additions such as biofuel. Therefore, the objective of the study was to evaluate the performance of two-phase anaerobic digestion of slaughterhouse wastewater in terms of biogas production, methane yield, and removal efficiencies of organic matter, total nitrogen, and total phosphorus. Two consecutively connected 40 L galvanized metal anaerobic batch bioreactors were used to conduct the experiment. The total phosphorus removal efficiencies of hydrolytic-acidogenic reactor and methanogenic reactor were 13.34% and 16.58%, respectively. Total chemical oxygen demand, soluble chemical oxygen demand, biological oxygen demand, total dissolved solids, total solids, total suspended solids, volatile solids, and turbidity had overall removal efficiencies of 82.87, 88.53, 93.32, 75.35, 95.55, 98.95, 97.42 and 98.06%, respectively. Biogas production of 189.45 mL/day with methane and carbon dioxide compositions of 67.69% and 29.9%, respectively, was also achieved. It was concluded that the two-phase anaerobic digestion of slaughterhouse wastewater shows substantial organic matter removal efficiencies and biogas production.

Improvement of the Sludge Decomposition and Nutrients Release by a Treatment with Potassium Permanganate Combined with an Ultrasonic Process

Ultrasonic decomposition of sludge is a popular method for sludge treatment. Potassium permanganate (KMnO4) was added to promote the reduction of sludge and hydrolysis efficiency. The effect of ultrasonic treatment (ULT) combined with potassium permanganate (KMnO4) preprocessing on the disintegration of waste activated sludge (WS) was studied in this survey. The results indicated that the combined pretreatment of KMnO4 and ULT (150 W, 20 min) significantly improved the decomposition efficiency and nutrient release efficiency of sludge. The volatile suspended solids (VSS) were lessened by 15.22%, which was 56.8% larger than that of raw sludge. The soluble proteins, soluble chemical oxygen demand (SCOD), polysaccharides, and volatile fatty acids (VFAs) were improved by 2005.1%, 464%, 669.8%, and 719.9% respectively. The deliquescent organic matter in sludge products also effectively decreased, demonstrating the effective promoting effect of KMnO4 + ULT. Mechanistic studies showed that ULT united with KMnO4 pretreatment could improve the biodegradability of soluble organic matter by generating reactive radicals, effectively disrupt the structure of cell walls, lyse extracellular polymers, and accelerate the liberation of organic matter. The composite sludge decomposition process further mitigates the harm of sludge to the environment and provides a cleaner and more efficient sludge reduction and utilization method.

Deconstruction of waste personal protective equipment (PPE) using subcritical wet air oxidation

Wet air oxidation (WAO) of the PPE mixture was performed at temperatures ranging from 300 °C to 350 °C, with initial air pressures of 30 bar and 60 bar, respectively. Total suspended solids (TSS) were reduced by up to 99%, while total chemical oxygen demand (tCOD) and soluble chemical oxygen demand (sCOD) were significantly reduced to 360 mg/L and 110 mg/L, respectively. The main products were volatile fatty acids such as acetic and propionic acids and ammonia nitrogen (NH3-N) with concentrations of up to 1117 mg/L, 975 mg/L, and 18 mg/L, respectively. Nitrogen and oxygen were the most abundant gaseous products, reaching 72% (w/w) and 14% (w/w), respectively. Semi-batch WAO treatments were carried out at 300 °C and 350 °C to achieve comparable waste reduction. The results suggest that non-catalytic WAO is a viable PPE waste management solution.

Effects of Magnetic Biochar Addition on Mesophilic Anaerobic Digestion of Sewage Sludge.

As a low-cost additive to anaerobic digestion (AD), magnetic biochar (MBC) can act as an electron conductor to promote electron transfer to enhance biogas production performance in the AD process of sewage sludge and has thus attracted much attention in research and industrial applications. In the present work, Camellia oleifera shell (COS) was used to produce MBC as an additive for mesophilic AD of sewage sludge, in order to explore the effect of MBC on the mesophilic AD process and its enhancement mechanism. Analysis by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectrometry (FTIR), and X-ray diffraction (XRD) further confirmed that biochar was successfully magnetized. The yield of biogas from sewage sludge was enhanced by 14.68-39.24% with the addition of MBC, and the removal efficiency of total solid (TS), volatile solids (VS), and soluble chemical oxygen demand (sCOD) were 28.99-46.13%, 32.22-48.62%, and 84.18-86.71%, respectively. According to the Modified Gompertz Model and Cone Model, the optimum dosage of MBC was 20 mg/g TS. The maximum methane production rate (Rm) was 15.58% higher than that of the control reactor, while the lag-phase (λ) was 43.78% shorter than the control group. The concentration of soluble Fe2+ and Fe3+ were also detected in this study to analyze the function of MBC for improving biogas production performance from sewage sludge. The biogas production was increased when soluble Fe3+ was reduced to soluble Fe2+. Overall, the MBC was beneficial to the resource utilization of COS and showed a good prospect for improving mesophilic AD performance.

Effects of hydrothermal pre-treatment on methane potential of anaerobic digestion sludge cake of cattle manure containing sawdust as bedding materials.

The purpose of this study was to analyze the effect of the hydrothermal pretreatment of anaerobic digestion sludge cake of cattle manure on the solubilization of organic matter and the methane yield in order to improve the anaerobic digestion efficiency of cattle manure collected from the sawdust pens of cattle. Anaerobic digestion sludge cake (ADSC) of cattle manure was thermally pre-treated at 160, 180, 200, and 220°C by the hydrothermal pressure reactor, and the biochemical methane potential of ADSC hydrolysate was analyzed. Methane yield recovered by the hydrothermal pre-treatment of ADCS was estimated based on mass balance. The COD solubilization degree (CODs) of the hydrothermal hydrolysate increased to 63.56, 67.13, 70.07, and 66.14% at the hydrothermal reaction temperatures of 160, 180, 200, and 220 °C, respectively. Considering the VS content obtained after the hydrothermal pretreatment, the methane of 10.2 Nm3/ton-ADSC was recovered from ADSC of 1.0ton, and methane yields of ADSC hydrolysate increased to 15.6, 18.0, 17.4, and 17.2 Nm3/ton-ADSC. Therefore, the optimal hydrothermal reaction temperature that yielded the maximum methane yield was 180 °C based on mass balance, and the methane yield from cattle manure containing sawdust was improved by the hydrothermal pre-treatment of ADSC.

A comparison of reactor configuration using a fruit waste fed two-stage anaerobic up-flow leachate reactor microbial fuel cell and a single-stage microbial fuel cell

Food waste generation and its consequent environmental impacts are increasing due to rapid urbanization, the global population, and associated food demand. Microbial fuel cells (MFCs) are a sustainable technology through which this food waste can be treated and used to produce bioelectricity. This study used two MFC configurations, a two-stage anaerobic up-flow leachate reactor MFC and a single-stage MFC, comparing the potential to treat solid fruit waste and fruit waste leachate. The two-stage MFC showed a higher potential to remove substrate at a shorter time compared to single-stage MFC. In 30 days, the two-stage anaerobic up-flow leachate reactor had a power density of 221 mW/m2. It was able to remove more total solids (by 95 %), volatile solids (by 70 %), total chemical oxygen demand (by 83 %), soluble chemical oxygen demand (by 87 %), and carbohydrates (by 33 %) compared to the single-stage MFC. However, the single-stage MFC showed higher coulombic efficiency (by 86.7 %) compared to the two-stage MFC. The efficiency of single-stage MFC improved by adding buffer and maintaining a neutral pH level of the substrate. The results of this study emphasize the importance of reactor design and demonstrate that MFC can be a viable technology to generate bioenergy from food waste.

Ultrasonication-enhanced biogas production in anaerobic digestion of waste active sludge: A pilot scale investigation

In this study, long-term pilot experiments were conducted to investigate the effects of ultrasonication (US) pretreatment on anaerobic digestion (AD) performance. Life cycling assessment (LCA) was used to assess energy efficiency and environmental impacts. With the response to 90-s US at 0.8 W/mL, the soluble COD concentrations increased by 359.0%, whereas the sludge particle size decreased by 56.7%. The positive effects of US increased biogas production by 15.0% and 25.6% at raw sludge VS/TS averages of 0.60 and 0.43, respectively. LCA results indicated that energy neutralization for US-AD was feasible, with a total energy balance of 461.3 kW·h/t DS because of increased energy recovery. The use of US pretreatment allowed for a more diverse microbial community in AD, thereby improving resilience to environmental fluctuations. Unfortunately, US-AD exhibited weak efficiency in inactivating pathogens and antibiotic resistance genes (ARGs), and US could hardly improve the AD control of pathogens carrying ARGs.

EDTA-enhanced alkaline anaerobic fermentation of landfill leachate-derived waste activated sludge for short-chain fatty acids production: Metals chelation and EPSs destruction

Alkaline anaerobic fermentation (AAF) of waste activated sludge (WAS) has been demonstrated to be promising for short-chain fatty acids (SCFAs) recovery. However, high-strength metals and EPSs in the landfill leachate-derived WAS (LL-WAS) would stabilize its structure, suppressing AAF performance. To improve sludge solubilization and SCFAs production, AAF was coupled with EDTA addition for LL-WAS treatment. The results show that sludge solubilization at AAF-EDTA was promoted by 62.8% than AAF, releasing 21.8% more soluble COD. The maximal SCFAs production of 477.4 mg COD/g VSS was thus achieved, i.e., 1.21 and 6.13 times those at AAF and the control, respectively. SCFAs composition was also improved with more acetic and propionic acids (80.8% versus 64.3%). Metals bridging EPSs were chelated by EDTA, which significantly dissolved metals from sludge matrix (e.g., 23.28 times higher soluble Ca than AAF). EPSs tightly bound with microbial cells were thus destructed (e.g., 4.72 times more protein release than alkaline treatment), causing an easier sludge disruption and subsequently a higher SCFAs production by hydroxide ions. These findings suggest an effective EDTA-supported AAF for metals and EPSs-rich WAS to recover carbon source.

Microbial community-based production of single cell protein from soybean-processing wastewater of variable chemical composition

The use of food-processing wastewaters to produce microbial biomass-derived single cell protein (SCP) is a sustainable way to meet the global food demand. Microbial community-based approaches to SCP production have the potential benefits of lower costs and greater resource recovery compared to pure cultures, yet they have received scarce attention. Here, SCP production from soybean-processing wastewaters using their existent microbial communities was evaluated. Six sequencing batch reactors of 4.5-L working volume were operated at 30 °C for 34 d in cycles consisting of 3-h anaerobic and 9-h aerobic phases. Four reactors received no microbial inoculum and the remaining two were amended with 1.5 L of a mixed culture from a prior SCP production cycle. Reactors produced more SCP when fed with wastewaters of higher soluble total Kjeldahl nitrogen (sTKN) content. The protein yield in biomass ranged from 0.53 to 3.13 g protein/g sTKN, with a maximum protein content of 50 %. The average removal of soluble chemical oxygen demand (sCOD) and soluble total nitrogen (sTN) was 92 % and 73 %, respectively. Distinct microbial genera were enriched in all six bioreactors, with Azospirillum, Rhodobacter, Lactococcus, and Novosphingobium dominating. The study showed that constituents in soybean wastewater can be converted to SCP and demonstrated the effect of variable influent wastewater composition on SCP production.

Pretreatment of Slaughterhouse Effluent Treatment Plant Sludge Using Electro-Fenton Process for Anaerobic Digestion

Sludge management is an integral process of an effluent treatment plant (ETP). This study aimed at using the electro-Fenton (EF) process for pretreatment of a cattle-based slaughterhouse ETP sludge to enhance biogas production from anaerobic digestion. EF-oxidation experiments were conducted in 0.5 L beakers with mild-steel electrodes, to study the effect of factors, viz., H2O2 concentration, current density and reaction time on soluble chemical oxygen demand (sCOD) concentration, soluble extracellular polymeric substances (sEPS) concentration and volatile suspended solids (VSS) removal efficiency. This was followed by the quantification of biogas production from the raw and pretreated sludge in anaerobic digestion (AD). Experimental conditions for the EF process were optimized using response surface methodology (RSM). At optimized experimental conditions, EF pretreatment resulted in an increase in sCOD and sEPS concentrations, from 0.91 g/L to 6.1 g/L and 0.18 g/L to 1.4 g/L, respectively. VSS removal efficiency was 68.1%. Batch anaerobic digestion studies demonstrated an enhancement in the specific biogas yield, from 110 NmL/g-VS to 460 NmL/g-VS.

Optimizing waste activated sludge disintegration by investigating multiple electrochemical pretreatment conditions: Performance, mechanism and modeling

The complex and rigid floc structure often limits the reutilization of waste activated sludge (WAS). Electrochemical pretreatment (EPT) is one of the most effective technologies that can enhance WAS disintegration. But a comprehensive investigation into how multiple EPT conditions work was rarely reported. The study evaluated the effects of multiple EPT conditions, i.e., different electrolytes (NaCl, Na2SO4, and CaCl2), electrolytes dosage (0 g/L, 0.5 g/L, 1.0 g/L, and 3.0 g/L), EPT current (0 A, 0.5 A, 1.0 A, and 3.0 A) and EPT time (0 min, 30 min, 60 min, and 90 min) on WAS disintegration. The results showed that NaCl was outstanding from other electrolytes in promoting more WAS disintegration. Besides, a relatively higher NaCl dosage, a higher EPT current, and a longer EPT time promoted more reactive chlorine species (RCS), thus enhancing WAS disintegration in terms of extracellular polymeric substances (EPS) structure destruction and biodegradable organic matter release. After EPT for 60 min at NaCl dosage of 1.0 g/L and current of 1.0 A, the EPS multilayer structure destruction, biodegradable organic matters release, and soluble chemical oxygen demand (SCOD) increase in the supernatant were enhanced by 17.2 %, 130.5 %, and 238.7 %, respectively. Then a predictive quadratic model was established and the impact significance of the above EPT factors for enhancing WAS disintegration followed dosage of NaCl > current > EPT time. Furthermore, response surface methodology (RSM) suggested NaCl dosage of 2.75 g/L, current of 2.0 A, and EPT time of 30 min were the optimal EPT conditions, bringing a 42.0 % increase in the net economic benefit of WAS treatment compared to without EPT.

Clean Monascus pigments production from Chinese rice wine wastes through submerged fermentation

The potential for Monascus pigments (MPs) production in a mixture of Chinese rice wine lees, soaked rice wastewater and broken rice was explored. MPs production reached 120.1 U/mL with optimal solid-liquid ratio of culture medium 1:10 and 20 g/L broken rice addition at shake flask level. We further explored the effects of stirring speed on MPs production in 7.5 L agitated bioreactor. The stirring speed had a great impact on cell morphology and the maximum MPs concentration and yield were 128.4 U/mL and 8174 U/g respectively at 400 rpm. The soluble chemical oxygen demand for the soaked rice wastewater decreased by 78.7%, which was mainly due to the intake of carbohydrates, organic acids and amino acids. Furthermore, a simultaneous fermentation process and production system with two-stage stirring speed control strategy was further developed in the 50 L pilot scale, in which the MPs production reached 158.9 U/mL. Meanwhile, Chinese rice wine wastes were fully utilized without addition of organic solvents during the process and no generation of new waste. Our results showed that Monascus was capable of converting Chinese rice wine wastes into natural pigments by submerged fermentation, which could provide an economic and environmentally friendly approach to reduce the cost of wastes treatment as well as high-value utilization.