Higher Soluble Chemical Oxygen Demand Research Articles

Optimum Magnetite–Zeolite Nanoparticles Loading on the Cathode of Microbial Electrochemical–Anaerobic Digestion System for Enhancing Methane Generation

Microbial electrochemical systems (MESs) can enhance methane production in anaerobic digestion, but their performance is hindered by inadequate electron transfer between the cathode and microbes. Magnetite–zeolite (MZ)‐based catalysts accelerate electron exchange; however, the optimal loading of MZ is crucial for maximizing MES performance. In this study, different loadings of the MZ catalyst ranging from 0 to 2 mg cm−2 on the cathode were evaluated to obtain an optimum loading for maximizing methane recovery from MES. Electrochemical analyses demonstrated enhanced electrochemical reduction kinetics of the cathode with increased MZ loading from 0 to 2 mg cm−2. Among the tested loadings, the MES with 1 mg cm−2 MZ on the cathode exhibited the highest methane production rate at 548 mL L−1 d−1, surpassing other MES operations with 2 and 0.5 mg cm−2 (499 and 434 mL L−1 d−1, respectively). Additionally, the MES with 1 mg cm−2 MZ demonstrated the highest soluble chemical oxygen demand removal efficiency of 87% and total coulomb recovery of 1444.06C ± 42.60C, with the lowest amount of volatile fatty acids accumulation. Consequently, MZ is recommended as a superior catalyst for enhancing MES performance and suggested to utilize 1 mg cm−2 MZ loading on the cathode to maximize methane production.

Enhanced methane yield in anaerobic digestion of waste activated sludge by combined pretreatment with fungal mash and free nitrous acid

This study explores a novel approach for enhancing anaerobic digestion of waste activated sludge (WAS) through the combined pretreatment of fungal mash and free nitrous acid (FNA). Aspergillus PAD-2, a fungal strain with superior hydrolase secretion, was isolated from WAS and cultivated in-situ on food waste to produce fungal mash. The solubilization of WAS by fungal mash achieved a high soluble chemical oxygen demand release rate of 548 mg L−1 h−1 within first 3 h. The combined pretreatment of fungal mash and FNA further improved the sludge solubilization by 2-fold and resulted in a doubled methane production rate of 416±11 mL CH4 g−1 volatile solids. The Gompertz model analysis revealed a higher maximum specific methane production rate and shortened lag time by the combined pretreatment. These results demonstrate that the combined fungal mash and FNA pretreatment offers a promising alternative for fast anaerobic digestion of WAS.

Anaerobic fermentation of aerobic granular sludge: Insight into the effect of granule size and sludge structure on hydrolysis and acidification

Aerobic granular sludge (AGS) has different physicochemical properties and microbial communities compared to conventional activated sludge (CAS), which may result in different behaviors during anaerobic fermentation and require further investigation. This study investigated the effect of granule size and sludge structure on the hydrolysis and acidification of AGS. Experimental results show that AGS exhibited significantly higher soluble chemical oxygen demand (SCOD) dissolution and total volatile fatty acids (TVFA) production (330.6–430.3 mg/gVSS and 231.0–312.5 mgCOD/gVSS) compared to conventional activated sludge (CAS) (167.0 mg/gVSS and 133.3 mgCOD/gVSS). This is because AGS (90.6–96.9 mg/gVSS) had higher extracellular polymeric substances (EPS) content than CAS (81.2 mg/gVSS). EPS can not only serve as substrates but also release the trapped hydrolases. Moreover, the relative abundances of hydrolytic/acidogenic bacteria and genes were higher in AGS (0.46%–3.60% and 3.01 × 10−3%-4.04 × 10−3%) than in CAS (0.30% and 1.23 × 10−3%). The optimal granule size for AGS fermentation was found to be 500–1600 μm. The crushing of granule structure promoted the dissolution of small amounts of EPS and the release of some trapped hydrolases, thereby potentially enhancing the enzyme-substrate contacts and bacteria-substrate interactions. Therefore, the highest SCOD dissolution (510.6 mg/gVSS) and TVFA production (352.1 mgCOD/gVSS) from crushed 500–1600 μm AGS were observed. Overall, the findings of this study provide valuable insights into the recovery of organic carbon from AGS via anaerobic fermentation.

A green co‐treatment to accelerate the hydrolysis of sludge during anaerobic fermentation using free nitrous acid and sodium citrate

AbstractBackgroundAnaerobic fermentation of waste activated sludge to produce short‐chain fatty acids (SCFAs) is one of the means of sludge resource utilization. However, the protective effect of the extracellular polymeric substances (EPS) structure contained in sludge flocs can lead to a slow hydrolysis process, which inhibits the production of SCFAs.ResultsIn this study, a new step‐by‐step pretreatment method for breaking sludge flocs was adopted. The cationic complexing agent sodium citrate (C6H5Na3O7) was used first to break the cationic bridging structure of EPS, and then the strong oxidizing property of free nitrous acid (HNO2) was used to break the cell structure. The results showed that the C6H5Na3O7 dose of 0.10 g g−1 total suspended solids (TSS) was able to disintegrate EPS, and the optimal dose and pretreatment time of HNO2 under these conditions were 2.504 mg L−1 and 24 h, respectively, when the highest soluble chemical oxygen demand (SCOD) content of 1700 ± 25 mg L−1 was reached. SCFA production in the group of 0.10 g g−1 TSS with 2.504 mg L−1 HNO2 co‐pretreatment reached 1827 ± 40 mg COD L−1 at 8 days of fermentation.ConclusionThe presence of C6H5Na3O7 accelerated the degradation rate of HNO2 during fermentation, and the pH fluctuation of the system was lower compared to the HNO2 pretreatment alone. Moreover, the synergistic pretreatment significantly changed the bacterial community structure within the system and Petrimonas (47.62%), belonging to the hydrogen and acetic acid‐producing bacteria, was enriched, which promoted organic matter degradation and SCFA production. These findings will contribute to optimization of the sludge treatment process. © 2023 Society of Chemical Industry (SCI).

Multi-angle evaluation of the anaerobic digestion of Molasses vinasse using two different feeding patterns

Molasses vinasse (MV) is a waste burden in alcohol production due to its high organic matter content. However, it represents a potential source of energy recovery if adequately treated. In this study, two feeding patterns (pulse feeding: 8 ​L/4 ​h and semi-continuous feeding: 8 ​L/23 ​h) were evaluated for their effects on MV anaerobic digestion from multiple perspectives in a laboratory-scale reactor. The results demonstrated that semi-continuous feeding not only achieved a higher soluble chemical oxygen demand (sCOD) removal rate of 78.48% but also increased the production of biogas and methane by 20.04% and 51.48%, respectively. In addition, the chemical composition analysis suggested that the semi-continuous feeding pattern degraded the majority of lignin/CRAM and aromatic substances more effectively than the pulse feeding pattern. Moreover, the microbial analysis revealed that semi-continuous feeding increased the number of dominant bacteria, including Chloroflexi, Synergistetes, and Cloacimonetea, and methanogenic archaea, including Methanosaeta and Methanosarcina. The findings of this study, therefore, confirm that the semi-continuous feeding model is more effective and has good application potential, laying the groundwork for the MV anaerobic industrial processes.

Phylogenomic analysis of Citrobacter sp. strain AAK_AS5 and its metabolic capabilities to support nitrogen removal behavior.

Despite the ubiquity of the genus Citrobacter in clinical, industrial, and environmental scenarios, a large number of Citrobacter strains have not been explored at the genome-scale level. In this study, accurate taxonomic assignment of strain AAK_AS5 isolated from activated sludge was achieved by in-silico genomic comparison using Overall Genome-based Relatedness Indices (ANI(OAT): 97.55%, ANIb:97.28%, and ANIm: 97.83%) that indicated its closest identity to the related strain Citrobacter portucalensis A60T . Results were consistent with a digital DNA-DNA hybridization value of 80% with C. portucalensis A60T which was greater than the species boundary value >70% for delineating closely related bacterial species. Gene mining through Kyoto Encyclopedia of Genes and Genomes (KEGG), and annotation using rapid annotation subsystem technology (RAST) revealed the notable gene contents for nitrogen metabolism and other pathways associated with nitrate/nitrite ammonification (28 genes), ammonia assimilation (22 genes), and denitrification pathways (14 genes). Furthermore, the strain AAK_AS5 also exhibited a high soluble chemical oxygen demand (sCOD), NH4 + -N, and NO3 - -N removal efficiency of 91.4%, 90%, and 93.6%, respectively thus validating its genetic capability for utilizing both (NH4 )2 SO4 and KNO3 as the nitrogen source. The study provided deeper insights into the phylogenomics and the genetic potential of Citrobacter, sp. strain AAK AS5 associated with nitrogen metabolism thus signifying the potential application of the isolate for treating nitrogen-rich wastewaters.

Enhanced anaerobic digestion for degradation of swine wastewater through a Fe/Ni-MOF modified microbial electrolysis cell

Stainless steel mesh, as the common cathode of microbial electrolytic cell-assisted anaerobic digestion (MEC-AD), has the disadvantages of low specific surface area, poor biocompatibility and low catalytic activity, which limits the production of methane. Metal-organic frameworks (MOFs) have attracted much attention due to their adjustable pores and specific catalytic properties. However, little attention was paid to the combination of MOF and stainless-steel mesh to improve the performance of MEC-AD cathode. In this study, we combined stainless steel mesh with bimetallic MOF catalyst (Fe/Ni–NH2BDC) to prepare a composite cathode, and verified its promoting effect on AD of swine wastewater. The experimental results showed that the reactor with the carbonized MOF composite cathode (FeNi2-PAN2) achieved the highest soluble chemical oxygen demand removal rate of 82.92% and a maximum cumulative methane yield of 213.47 mL CH4/g COD under an applied voltage of 0.8 V, which were 33.14% and 57.56% higher than those of an anaerobic digestion (AD) control reactor, respectively, and higher than those of a carbon paper (CP) cathode reactor. The enrichment of Methanobacterium and Methanoculleus on the surface of FeNi2-PAN2 cathode surface indicated that FeNi2-PAN2 cathode enhanced hydrogenotrophic methanogenesis and improved the stability of AD.

Integrating electrochemical pretreatment (EPT) and side-stream sulfidogenesis with conventional activated sludge process: Performance, microbial community and sludge reduction mechanisms

• Coupling EPT and sulfidogenic side-stream reactor (ESSR) with CAS process was studied. • EPT at 15 V/5min with 125 mg S/L of SO 4 2− dosage improved sludge reduction. • The ESSR could be designed with a very short SRT of 2.5 days. • The integrated process (ESSR-CAS) was operated over 200 d with good performance. • Possible reasons for fast sludge hydrolysis in ESSR-CAS were discussed. Recently, inserting an anaerobic side-stream reactor into a conventional activated sludge (CAS) process for upgrading biological wastewater treatment plants with in-situ sludge reduction function has been extensively studied. A typical example is an oxic-settling anaerobic (OSA) process, which can achieve efficient sludge reduction, but requires ample space, limiting its application potential. Optimizing the conventional OSA process towards compact and energy-efficient is necessary. This paper studied a new method by integrating electrochemical pretreatment (EPT) and sulfidogenesis-enhanced anaerobic treatment with a conventional OSA process to achieve considerable in-situ sludge reduction with a limited side-stream size requirement (i.e. short sludge retention time (SRT)). The proposed idea was verified experimentally – first, batch experiments were conducted to determine the effective sulfate concentration for the EPT and sulfidogenic side-stream reactor (ESSR); then, the ESSR-CAS process (upgrading CAS with a new ESSR) and a stand-alone CAS process (control) were operated in parallel for 200 days. The experimental results showed that: The new ESSR, with approximately 125 mg S/L of sulfate dosed and 5 min electrochemical sludge pretreatment at 15 V, can successfully accelerate anaerobic reactions, resulting in a short SRT of 2.5 days. The ESSR-CAS process can reduce sludge production by 61%, with high soluble chemical oxygen demand (SCOD) and total nitrogen (TN) removal efficiencies of 96% and 70% respectively. The possible mechanisms of ESSR for the augment of sludge hydrolysis (sludge floc disintegration, extracellular polymer destruction, and cell structure breakage) as well as the economic considerations of this new sulfur-cycle bioprocess are discussed.

Effect of air nanobubbles on oxygen transfer, oxygen uptake, and diversity of aerobic microbial consortium in activated sludge reactors

Nanobubbles have the potential to curtail the loss of oxygen during activated sludge aeration due to their extensive surface areas and lack of buoyance in solution. In this study, nanobubble aeration was explored as a novel approach to enhance aerobic activated sludge treatment and benchmarked against coarse bubble aeration at the lab scale. Nanobubble aerated activated sludge reactors achieved greater dissolved oxygen levels at faster rates. Higher soluble chemical oxygen demand removal by 10% was observed when compared to coarse bubble aeration with the same amount of air. The activated sludge produced compact sludge yielding easier waste sludge for subsequent sludge handling. The samples showed fewer filamentous bacteria with a lower relative abundance of floc forming Corynebacterium, Pseudomonas, and Zoogloea in the sludge. The microbiome of the nanobubble-treated activated sludge showed significant shifts in the abundance of community members at the genus level and significantly lower alpha and beta diversities.

Enhancement of Methane Production in Anaerobic Digestion of Food Waste using Thermal Pretreatment

Anaerobic digestion (AD) is an energy production process and food waste is a potential feedstock. The main biochemical reactions are Hydrolysis, Acidogenesis, Acetogenesis, and Methanogenesis. The hydrolysis step acts as the rate-limiting reaction and the pretreatment of the feedstocks can be used to support this step. In this research, thermal pretreatment was used as a potential method for food waste pretreatment. Six different pretreatment conditions were used: two different temperatures (80oC and 100oC) and three different pretreatment times (30, 60, and 90 min). The Bio-Methane Potential (BMP) test was conducted using 120 mL serum bottles for 20 days to determine the most suitable pretreatment conditions. An experiment was also conducted at the selected optimal conditions (80oC for 90 min) using a small-scale bioreactor against the control with a NaHCO3 buffer solution. The highest Soluble Chemical Oxygen Demand (SCOD) was observed at 100oC for 90 min. The optimal pretreatment was selected as 80oC for 90 min, which produced 14.75 mL/g VS of methane while the control produced 8.64 mL/g VS in BMP test. After a few days, the methane production started to slow down due to a decrease in pH. When a buffer was added, a specific methane yield of 120.13 mL/g VS was observed in the small-scale bioreactor. This was an 11.24% increase compared to the buffered control without thermal pretreatment. In conclusion, thermal pretreatment has a potential to enhance the AD but it is economical to use with less biodegradable waste than food waste.

Enhancing the decomposition of extracellular polymeric substances and the recovery of short-chain fatty acids from waste activated sludge: Analysis of the performance and mechanism of co-treatment by free nitrous acid and calcium peroxide

At present, the bioproduction of short-chain fatty acids (SCFAs) from waste activated sludge (WAS) has attracted worldwide attention due to the demand of carbon neutrality during waste treatment. Calcium peroxide (CaO2) has been reported to be an effective method for the solubilization of WAS and the accumulation of SCFAs, but the high reagent cost limits its industrial application. Therefore, free nitrous acid (FNA) was introduced into the WAS pretreatment system to assist with CaO2 for enhancing the disruption of extracellular polymeric substances (EPS) and the subsequent acidogenesis process. The results showed that FNA and CaO2 synergistically enhanced EPS decomposition and the release of biodegradable organic compounds during pretreatment. The highest soluble chemical oxygen demand (3.1- and 2.6-fold higher compared to individual pretreatments at the same concentrations) after pretreatment and the highest SCFAs accumulation (2.0- and 6.4-fold compared to individual pretreatments at the same concentrations) after a 2-day fermentation period was observed in the FNA + CaO2 (0.15 g/g VSS) co-treated group. Therefore, the FNA + CaO2 (0.15 g/g VSS) co-treatment was determined to be the optimal strategy for ensuring the disintegration of the EPS matrix and enhancing the accumulation of SCFAs in pretreated sludge during anaerobic digestion.

Energetic Valorization of Cereal and Exhausted Coffee Wastes Through Anaerobic Co-digestion With Pig Slurry

In the past years, there has been steady growth in work relating to improve resource efficiency through waste minimization and bioenergy recovery to mitigate climate change. Agro-food industries produce large amounts of bio-waste, challenging innovative energetic valorization strategies in the framework of circular economy principles. Anaerobic digestion (AD) technology is an interesting route to stabilize organic matter and produce biogas as a renewable energy source. This study involves continuous co-digestion of pig slurry (PS), cereal and exhausted coffee wastes (CECW) performed in a continuously stirred tank reactor, with a hydraulic retention time (HRT) of 16 days under at mesophilic conditions (36.9 ± 0.3°C). The experimental trials, were designed to include different cereal and exhausted coffee liquor (CECL) shares in the feeding mixture, corresponding to different PS to CECL ratios (PS:CECL), respectively: 100:0 (T0), 90:10 (T1), 80:20 (T2), and 70:30 (T3), in terms of percentage of inlet feeding rate (v:v). The results obtained for the feeding rate (70:30) yield to the highest specific methane production (SMP = 341 ml.gVS−1) led to a 3.5-fold improvement in comparison with the reference scenario. The synergetic effect between the microbial consortia of PS and the high carbon to nitrogen ratio (C/N) of CECL explain the improvements achieved. The maximum soluble chemical oxygen demand (SCOD) reduction (84.0%) due to the high content and soluble chemical oxygen demand to total chemical oxygen demand ratio (SCOD/TCOD) corroborate the results achieved. The digester stability, evaluated by specific energetic loading rate, was below the limit (0.4 d−1). Results from ANOVA showed a significant effect of CECL on the resulting GPR and SMP values. Additionally, Tukey's “Honest Significant Difference” method, confirmed statistically significant differences between the trials T3-T0, T3-T1, T3-T2, and T2-T0. Thus, co-digestion of PS and of CECL seems to be a promising approach for bioenergy recovery and promoting biowastes circularity.

Influence of dilute acid, alkali and hydrothermalpretreatments on methane improvement from datepalm waste “Takarboucht” cultivar

This research assesses the impacts of hydrothermal (120 °C for 30 min), dilute acid (2%(w/w) H2SO4 at 120 °C for 30 min) and alkali (6% (w/w) NaOH at 35 °C for 24 h)pretreatments on the methane yield from date palm waste “Takarboucht” cultivar. The pretreated and untreated date palm waste (DPW) were digested at mesophilic temperature (36 °C) for 20 days. The highest soluble chemical oxygen demand (sCOD) was obtained by DPW hydrolysate from alkali pretreatment. The highest methane yield of 161.86 ml/g VS was obtained from untreated DPW. Among all pretreatments, higher methane yield was obtained from hydrothermally pretreated DPW (153.35 ml/g VS), followed by acid pretreated DPW (141.65 ml/g VS) and alkali pretreated DPW (50.78 ml/g VS). Alkali pretreatment improved the solubilization of DPW, however, it may not necessarily provide an enhancement in the methane yield. The optimization of the conditions of each pretreatment is proposed.

Bioenergy production and treatment of aquaculture wastewater using saline anode microbial fuel cell under saline condition

Saline anode microbial fuel cell (SA-MFC) equipped with carbon felt as anode and cathode, separated by nafion membrane was used to evaluate the aquaculture wastewater treatment efficiency and energy production under saline condition (4%). Operation of SA-MFC was executed at different organic load (OL) from 0.5 gCOD/L to 1.5 gCOD/L under saline condition. TCOD (Total Chemical Oxygen Demand) removal was 75 ± 1.4%, 81 ± 0.9% and 84 ± 1.1% at 0.5, 0.75 and 1 gCOD/L OL respectively. SCOD (Soluble Chemical Oxygen Demand) removal in SA-MFC was 68 ± 1.2%, 75 ± 0.8% and 81 ± 0.5% at 0.5, 0.75 and 1 g COD/L OL. Among the OL used 1.25 gCOD/L recorded high TCOD (92 ± 1.1%), SCOD (91 ± 0.5%) and TSS (Total Suspended Solids) removal (78 ± 0.7%) with a maximum power production (369 mW/m 2 ). Increase in OL to 1.5 gCOD/L revealed decline in TCOD (79 ± 1.3%), SCOD (74 ± 0.8%), TSS (71 ± 1.5%) removal and power production (310 mW/m 2 ). The predominant bacterial strains responsible for aquaculture wastewater treatment and energy production was identified as Ochrobactrum (53%), Marinobacter (22%) and Rhodococcus (15%). The other strains such as Bacillus , Stenotrophomonas , Xanthobacter , Sphingomonas , Pseudomonas and Sedimentibacter also present in the SA-MFC reactor operated under saline condition. • Treatment of aquaculture wastewater in SA-MFC under saline condition (4%). • TCOD and SCOD removal was 92 and 91% at 1.25 gCOD/L OL. • Maximum power density of 369 mW/m 2 at 1.25 OL. • Dominance of Ochrobactrum, Marinobacter and Rhodococcus in SA-MFC.

The effect of hydrothermal treatment on industrial wastewater: Hungary as a case study

AbstractIndustrial wastewater is a growing environmental challenge due to its high concentrations of organics and its limited biological degradability. Up to date, however, no published work discussed industrial wastewater characterization, which is the focus of this study. Moreover, the effect of hydrothermal treatment on the chemical oxygen demand (COD) removal and the soluble chemical oxygen demand (SCOD) release was investigated in this work. Wastewater samples were collected from different industrial sites and characterized in order to determine their initial properties. It was summarized that the salinity of wastewater estimated by EC was relatively low, and its pH values were in the acceptable range. On the other hand, however, high values of sodium absorption ratio (SAR) were obtained in all samples post to hydrothermal treatment. Nonetheless, our results revealed higher SCOD release post to hydrothermal treatment suggesting better efficiency of COD removal obtained by this treatment technique.

Treatment of chocolate-processing industry wastewater in a low-temperature pilot-scale UASB: Reactor performance and in-situ biogas use for bioenergy recovery

The main objectives of this research were twofold: a) to evaluate the performance of a low-temperature pilot-scale upflow anaerobic sludge blanket (UASB) reactor during the treatment of a chocolate-processing industry wastewater (CIW) with high soluble chemical oxygen demand; and b) to evaluate the performance of two thermal conditioning devices (TCDs) for bioenergy recovery through the in-situ biogas use. For 275 days, the UASB reactor was operated at low temperature (17–19 °C), short hydraulic retention time (6.2 h) and variable total organic loading rate (OLRT) and soluble organic loading rate (OLRS) (10.3 ± 2.9 kg-CODΤ/m3/d and 7.9 ± 2.2 kg-CODS/m3/d, respectively). The produced biogas was burned in-situ with two TCDs, which mainly consisted of an insulated combustion chamber, a heat exchanger and a Bunsen burner. The OLRT and OLRS removal efficiencies were 59.5 ± 13.6% and 71.4 ± 13.2%, respectively, whereas the biogas production was in the range of 119–834 L/d. In-situ burning of the produced biogas with the TCDs increased the influent temperature between 0.8 and 5.8 °C, which improved the biogas production of the UASB reactor. The CIW energetic potential was calculated based on the UASB reactor operational parameters, the calorific value of methane in biogas and the daily CIW production (90 m3) of the studied factory. The estimated CIW energetic potential (13.59 MJ/m3CIW) represents a sustainable source of energy, which could be enough to satisfy the power consumption of 25–42 households in Toluca Valley Metropolitan Area, Mexico.

Anaerobic bio-methane potential of the liquors from hydrothermal carbonization of different lignocellulose biomasses

In this work, the spent liquor of pine sawdust (L1), canola oil waste (L2), olive oil waste (L3) and vineyards waste (L4) from hydrothermal carbonization (220 °C, 1 h) process were studied as substrates for biogas production. Kinetic degradation using three kinetic models (Gompertz model, Hill model and Chapman model) was also analyzed. The batch experiments showed that the highest methane yield (253 NmLCH4/gCODadded) and higher soluble Chemical Oxygen Demand (sCOD) removal efficiency (71%) was achieved for the spent liquor of L1, reaching up to 81% of the theoretical methane yield. The liquid fractions of L2, L3 and L4 resulted in lower yields (24 ̶ 36% of the theoretical yield) and lower sCOD removal (40 ̶ 45%), which can be related to the presence of recalcitrant nitrogen materials formed during the HTC. Gompertz model better represents the performance of the liquor fractions (L1 and L2), having long lag phase (5–7 days), while Chapman model adjusted the accuracy of the behavior of L3 and L4 (lag phase < 1 days). As a conclusion, the spent liquor coming from HTC process of lignocellulosic biomass waste can be used as resource to recover energy through anaerobic digestion.

Does the combined free nitrous acid and electrochemical pretreatment increase methane productivity by provoking sludge solubilization and hydrolysis?

Free nitrous acid based pretreatments are novel and effective chemical strategies for enhancing waste activated sludge solubilization. In this study, the synergetic effects of the combined free nitrous acid and electrochemical pretreatment on sludge solubilization and subsequent methane productivity were evaluated. The results indicated that pretreatment with 10 V plus 14.17 mg N/L substantially enhanced sludge solubilization, with the highest soluble chemical oxygen demand concentration of 3296.7 mg/L, 25.6-time higher than that without pretreatment (128.9 mg/L). Due to the potential toxicity of NO2− and NO3− to microorganisms and its bioprocesses, the methane production of sludge pretreated by free nitrous acid was significantly deteriorated. The maximum methane yield (152.0 ± 9.6 mL/g-VSadded) was observed at 10 V pretreatment alone, only 1.7% higher than that of the control (149.4 ± 1.6 mL/g-VSadded). Combined pretreatment indeed enhances the sludge solubilization and hydrolysis, but does not always induce an improved anaerobic digestion efficiency.

Coagulation-flocculation and moving bed biofilm reactor as pre-treatment for water recycling in the petrochemical industry.

Water recycling and reuse is of important value in water-using sectors like petrochemical industry. The aim of this research was to optimise the pre-treatment of petrochemical wastewater to undergo a further membrane treatment, with the final objective of water recycling within the same industry. Laboratory coagulation-flocculation tests prior to biological treatment were performed using Actiflo® Veolia commercial technology and an optimal coagulant dose of 30 mg/L ferric chloride was obtained. A bench-scale Moving Bed Biofilm Reactor (MBBR) system with two sequential reactors with working volumes of 5 L was filled with Z-carriers at 35% of their working volume. Organic loading rate (OLR) was varied from 0.2 to 3.25 kg/(m3 d) and the hydraulic retention time (HRT) ranged from 23.4 h to 4.5 h. High soluble chemical oxygen demand (sCOD) removals were obtained in stationary states (80-90%) and the calculated maximum sCOD that the system could degrade was 4.96 ± 0.01 kg/(m3 d) at 23 ± 2 °C. Changes in feed composition did not decrease sCOD removals showing that MBBR is a robust technology and the coagulation-flocculation step could be by-passed. Further removal of total suspended solids (TSS) and turbidity from the MBBR effluent would be required before a reverse osmosis (RO) step could be performed. A biofilm-forming genus, Haliscomenobacter spp., and an oil degrading genus Flavobacterium spp. were found in all the attached biomass samples. Acinetobacter spp. was the major bacterial genera found in suspended biomass. Proteobacteria and Bacteroidetes were the major phyla detected in the carrier samples while Proteobacteria the main one detected in the suspended biomass. The lack of fungal annotated sequences in databases led to a major proportion of fungal sequences being categorized as unclassified Fungi. The results obtained indicate that MBBR is an appropriate technology for hydrocarbon-degrading microorganism growth and, thus, for petrochemical wastewater pre-treatment for water regeneration.

Bioelectrochemically-assisted vermibiofilter process enhancing stabilization of sewage sludge with synchronous electricity generation

Bioelectrochemically-assisted vermifilter (VBFBE) with sewage sludge as the anode fuel was constructed to accelerate composting of sewage sludge, which could increase the quality of the compost and harvest electric energy in comparison with vermicomposting and electrochemical only. Results revealed that the sludge stabilization with a higher soluble chemical oxygen demand (SCOD) and lower NH4+-H during 40 days of composting. At the composting, pH, C/N, electrical conductivity (EC) and germination index (GI) results demonstrated that the maturity degree of VBFBE4 was higher than that of other VBFBE. The VBFBE4 yielded a voltage of 1.024 V and maximum power density of 105.28 mW/m2 on 3th day. The bacteria in VBFBE4 were richer and higher in terms of diversity than those in other VBFBE, that was demonstrated that combination vermicomposting and electrochemistry could improve the sludge stabilization degree, accelerate sludge composting process and enhance composting maturity.