Continuous fermentation of food waste leachate for the production of volatile fatty acids and potential as a denitrification carbon source

A membrane bioreactor with iron dosing and acidogenic co-fermentation for enhanced phosphorus removal and recovery in wastewater treatment

A novel phosphorous (P) removal and recovery process using a membrane bioreactor (MBR) with ferric iron dosing and acidogenic co-fermentation was developed for municipal wastewater treatment. The very different solubility of Fe(III)-P and Fe(II)-P complex and the microbial transformation of Fe(III) to Fe(II) were utilized for P removal and recovery. By means of Fe-induced precipitation, chemical P removal was effectively achieved by an MBR with a flat-plate ceramic membrane; however, the Fe(III)-P solids accumulated in the MBR that constituted a significant fraction of the activated sludge. Anaerobic co-fermentation of the MBR sludge and food waste in a side-stream allowed the extraction of P and Fe from the sludge into the supernatant. The P in the supernatant was recovered as a fertilizer resource, while the sludge was returned to the MBR tank. The experimental results show that by adding FeCl₃ at 20 mg Fe/L into the influent of domestic wastewater, about 95.6% of total P could be removed by the MBR. One fifth (20%) of the sludge in the MBR was circulated daily through the side-stream fermenters for co-fermentation with cooked rice as the model food waste. The sludge underwent acidogenesis and dissimilatory iron reduction, resulting in a drop of the pH to below 5.0 and reduction of Fe(III) to Fe(II). Owing to the high solubility of the Fe(II)-P complex, P and Fe were then dissolved and released from the sludge into the supernatant. By simply adjusting the solution pH to 8.0, the P and Fe(II) in the supernatant readily re-precipitated to form vivianite for the P recovery. Using the iron dosing MBR and side-stream sludge fermentation, an overall P recovery efficiency of 62.1% from wastewater influent can be achieved, and the problem of inorganic build-up in the MBR is effectively alleviated.

Effects of C/N ratio on the performance of a hybrid sponge-assisted aerobic moving bed-anaerobic granular membrane bioreactor for municipal wastewater treatment

This study aimed to evaluate the impact of C/N ratio on the performance of a hybrid sponge-assisted aerobic moving bed-anaerobic granular membrane bioreactor (SAAMB-AnGMBR) in municipal wastewater treatment. The results showed that organic removal efficiencies were above 94% at all C/N conditions. Nutrient removal was over 91% at C/N ratio of 100/5 but was negatively affected when decreasing C/N ratio to 100/10. At lower C/N ratio (100/10), more noticeable membrane fouling was caused by aggravated cake formation and pore clogging, and accumulation of extracellular polymeric substances (EPS) in the mixed liquor and sludge cake as a result of deteriorated granular quality. Foulant analysis suggested significant difference existed in the foulant organic compositions under different C/N ratios, and humic substances were dominant when the fastest fouling rate was observed. The performance of the hybrid system was found to recover when gradually increasing C/N ratio from 100/10 to 100/5.

Recovery of phosphorus and volatile fatty acids from wastewater and food waste with an iron-flocculation sequencing batch reactor and acidogenic co-fermentation

A sequencing batch reactor-based system was developed for enhanced phosphorus (P) removal and recovery from municipal wastewater. The system consists of an iron-dosing SBR for P precipitation and a side-stream anaerobic reactor for sludge co-fermentation with food waste. During co-fermentation, sludge and food waste undergo acidogenesis, releasing phosphates under acidic conditions and producing volatile fatty acids (VFAs) into the supernatant. A few types of typical food waste were investigated for their effectiveness in acidogenesis and related enzymatic activities. The results show that approximately 96.4% of total P in wastewater was retained in activated sludge. Food waste with a high starch content favoured acidogenic fermentation. Around 55.7% of P from wastewater was recovered as vivianite, and around 66% of food waste loading was converted into VFAs. The new integration formed an effective system for wastewater treatment, food waste processing and simultaneous recovery of P and VFAs.

Use of food waste-recycling wastewater as an alternative carbon source for denitrification process: A full-scale study

Using organic wastes as an alternative to commercial carbon sources could be beneficial by reducing costs and environmental impacts. In this study, food waste-recycling wastewater (FRW) was evaluated as an alternative carbon source for biological denitrification over a period of seven months in a full-scale sewage wastewater treatment plant. The denitrification performance was stable with a mean nitrate removal efficiency of 97.2%. Propionate was initially the most persistent volatile fatty acid, but was completely utilized after 19days. Eubacteriacea, Saprospiraceae, Rhodocyclaceae and Comamonadaceae were the major bacterial families during FRW treatment and were regarded as responsible for hydrolysis (former two) and nitrate removal (latter two) of FRW. These results demonstrate that FRW can be an effective external carbon source; process stabilization was linked to the acclimation and function of bacterial populations to the change of carbon source.

Mitigating inhibition of undissociated volatile fatty acids (VFAs) for enhanced sludge-rice bran composting with ferric nitrate amendment

This study investigated the effect of ferric nitrate on mitigating the inhibition of volatile fatty acids (VFAs) during the initial phase of sewage sludge composting amended with rice bran. During the 34-day lab-scale composting, the supplementation of ferric nitrate enhanced the degradation of VFAs by up to 3 times as compared to the control. The organic matters loss (OML) rate in the treatment reactor was almost doubled with supplementation of ferric nitrate as compared to the control reactor during the initial phase. Eventually the treatment reactor achieved a 39.0% OML by the end of composting, which was 22% higher than the control. Ferric nitration addition mitigated the inhibition of VFAs by stimulating denitrification which consumed protons and VFAs. Ferric nitrate addition also decreased the electrical conductivity by 23% in the final compost product, reducing the possibility of phytotoxicity issue upon soil application. In summary, the results demonstrated that ferric nitrate addition could be an effective strategy for enhanced sludge composting.

Selective VFA production potential from organic waste streams: Assessing temperature and pH influence

This study explored the volatile fatty acid (VFA) production potential of seven waste streams from urban and agroindustrial sources. For that purpose, batch assays were performed under acidic (pH 5.5) and alkaline (pH 10) conditions at both mesophilic (35°C) and thermophilic (55°C) temperature. Overall, the VFA yield was influenced by temperature, and it was positively affected by pH, ranging between 220 and 677mgCODg^-1COD_fed for liquid waste streams and between 127 and 611mgCODg^-1COD_fed for solid waste streams and urban sludge. The highest VFA concentration and highest VFA/sCOD ratio was obtained during the organic fraction of municipal solid waste (OFMSW) fermentation, with 8,320mgCODL^-1 and 94% at alkaline pH and mesophilic temperature. The results of this study suggest that selective VFA production, i.e. via propionic, butyric and acetic acid production, might be feasible for scaling-up purposes with specific waste streams by adjusting the process parameters.

Heterotrophic nitrification and aerobic denitrification by Diaphorobacter polyhydroxybutyrativorans SL-205 using poly(3-hydroxybutyrate-co-3-hydroxyvalerate) as the sole carbon source

A new strain of Diaphorobacter polyhydroxybutyrativorans (strain SL-205) was recently isolated and identified. SL-205 can utilize nitrate and nitrite for denitrification and ammonium for nitrification using poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) as the carbon source under aerobic conditions. SL-205 removed 99.11% of NH₄⁺-derived N (83.90mg/L), 95.02% of NO₃^--N (308.24mg/L), and 84.13% of NO₂^--N (211.70mg/L), with average removal rates of 1.73mg NH₄⁺-N/(L·h), 6.10mg NO₃^--N/(L·h), and 4.95mg NO₂^--N/(L·h). Nitrogen gas was the primary end-product, with negligible nitrous oxide accumulation during ammonium removal, accounting for 57.85% of the removed NH₄⁺-N and 52.30% of the initial NH₄⁺-N. Moreover, hydroxylamine oxidoreductase, nitrate reductase, and nitrite reductase were detected, further indicating that strain SL-205 underwent heterotrophic nitrification coupled with aerobic denitrification (NH₄⁺→NH₂OH→NO₂^-→NO₃^-→NO₂^-→N₂O→N₂). These results support the use of PHBV as a carbon source for nitrogen removal from water and wastewater by strain SL-205.

Study on substrate metabolism process of saline waste sludge and its biological hydrogen production potential

With the increasing of high saline waste sludge production, the treatment and utilization of saline waste sludge attracted more and more attention. In this study, the biological hydrogen production from saline waste sludge after heating pretreatment was studied. The substrate metabolism process at different salinity condition was analyzed by the changes of soluble chemical oxygen demand (SCOD), carbohydrate and protein in extracellular polymeric substances (EPS), and dissolved organic matters (DOM). The excitation-emission matrix (EEM) with fluorescence regional integration (FRI) was also used to investigate the effect of salinity on EPS and DOM composition during hydrogen fermentation. The highest hydrogen yield of 23.6 mL H₂/g VSS and hydrogen content of 77.6% were obtained at 0.0% salinity condition. The salinity could influence the hydrogen production and substrate metabolism of waste sludge.

Enhanced methane production by semi-continuous mesophilic co-digestion of potato waste and cabbage waste: Performance and microbial characteristics analysis

Anaerobic granular sludge was used as an inoculum for co-digestion of potato waste (PW) and cabbage waste (CW) in batch and semi-continuous modes at 37±1°C for enhanced methane generation. Batch test results indicated that an equal proportion (1:1) by volatile solid was the optimal mixing ratio for co-digestion of PW and CW. Semi-continuous co-digestion process results showed that the stepwise increasing of the organic loading rates from 1.0 to 5.0kgVS/m³·d improved the methane yield from 224 to 360mL/g-VS. And the highest value was respectively 18.4% and 24.1% higher as compared to the mon-digestion of PW and CW. Further investigation with high-throughput sequencing analysis revealed that the enhanced methane generation was attributed to the partial shift from archaeal Methanosaeta to Methanosarcina and Methanobacterium, and from bacterial Firmicutes to Bacteroidetes and Proteobacteria. The volatile fatty acids concentration accounted for the modification of microbial communities.

Slowly released carbon source from composite materials system for removing nitrate pollution in groundwater

Chemoheterotrophic denitrification technologies using biopolymers as a solid carbon source and biofilm carriers have been widely trialed to remove nitrate from groundwater.

Influence of temperature and hydraulic retention on the production of volatile fatty acids during anaerobic fermentation of cow manure and maize silage

The aim of this study was to verify the efficiency of a separate hydrolysis step by testing different working temperatures (37-55°C) and hydraulic retention times (two, four and six days) and by evaluating readily biodegradable carbon production. The fermentation products included primarily acetic, propionic and butyric acids. These acids can be easily converted into biogas or can be recovered in a biorefinery approach, for example, to produce polyhydroxyalkanoates. The optimal condition was found by applying an organic loading rate of 17.9gTVSm^-3 with a four-day retention time at 37°C for an acidification yield of 183.2gCOD_VFAkgVS_fed^-1.

The role of methanogens in acetic acid production under different salinity conditions

In this study, a fed-batch acidogenic reactor was operated at a 3 d hydraulic retention time (HRT) and fed with alkaline pre-treated sludge to investigate salinity effects on methanogens' abundance, activities and their consumption of produced acetic acid (HAc) and total volatile fatty acids (VFAs). The salinity concentration was increased step-wise by adding sodium chloride. At 3‰ (parts per thousand) salinity, the average produced volatile fatty acids (VFAs) concentration was 2410.16 ± 637.62 mg COD L(-1) and 2.70 ± 0.36 L methane was produced daily in the acidogenic reactor. Further batch tests indicated methanogens showed a HAc degradation rate of 3.81 mg COD g(-1) VSS h(-1) at initial HAc concentration of 1150 mg COD L(-1), and showed tolerance up to 16‰ salinity (3.76 g Na(+) L(-1)) as indicated by a constant HAc degradation rate. The microbiological study indicated this can be related to the predominance of acetate-utilizing Methanosarcinaceae and Methanomicrobiales in the reactor. However, with salinity increased to 20‰ and 40‰, increases in VFAs and HAc production and decreases in methane production, methanogens population, acidogenic bacteria population and acidification extent were observed. This study demonstrated presence of acetate-utilizing methanogens in an acidogenic reactor and their high tolerance to salinity, as well as their negative impacts on net VFAs production. The results would suggest the presence of methanogens in the acidogenic reactor should not be ignored and the recovery of methane from the acidogenic reactor needs to be considered to avoid carbon loss.

Modeling and optimization of anaerobic codigestion of potato waste and aquatic weed by response surface methodology and artificial neural network coupled genetic algorithm

A novel approach to overcome the acidification problem has been attempted in the present study by codigesting industrial potato waste (PW) with Pistia stratiotes (PS, an aquatic weed). The effectiveness of codigestion of the weed and PW was tested in an equal (1:1) proportion by weight with substrate concentration of 5g total solid (TS)/L (2.5gPW+2.5gPS) which resulted in enhancement of methane yield by 76.45% as compared to monodigestion of PW with a positive synergistic effect. Optimization of process parameters was conducted using central composite design (CCD) based response surface methodology (RSM) and artificial neural network (ANN) coupled genetic algorithm (GA) model. Upon comparison of these two optimization techniques, ANN-GA model obtained through feed forward back propagation methodology was found to be efficient and yielded 447.4±21.43LCH4/kgVSfed (0.279gCH4/kgCODvs) which is 6% higher as compared to the CCD-RSM based approach.

Biogas generation in anaerobic wastewater treatment under tetracycline antibiotic pressure

The effect of tetracycline (TC) antibiotic on biogas generation in anaerobic wastewater treatment was studied. A lab-scale Anaerobic Baffled Reactor (ABR) with three compartments was used. The reactor was operated with synthetic wastewater in the absence of TC and in the presence of 250 μg/L TC for 90 days, respectively. The removal rate of TC, volatile fatty acids (VFAs), biogas compositions (hydrogen (H₂), methane (CH₄), carbon dioxide (CO₂)), and total biogas production in each compartment were monitored in the two operational conditions. Results showed that the removal rate of TC was 14.97–67.97% in the reactor. The presence of TC had a large negative effect on CH₄ and CO₂ generation, but appeared to have a positive effect on H₂ production and VFAs accumulation. This response indicated that the methanogenesis process was sensitive to TC presence, but the acidogenesis process was insensitive. This suggested that the presence of TC had less influence on the degradation of organic matter but had a strong influence on biogas generation. Additionally, the decrease of CH₄ and CO₂ generation and the increase of H₂ and VFAs accumulation suggest a promising strategy to help alleviate global warming and improve resource recovery in an environmentally friendly approach.