Chuanfu Wu

A comprehensive review on food waste anaerobic digestion: research updates and tendencies.

Anaerobic digestion has been practically applied in agricultural and industrial waste treatment and recognized as an economical-effective way for food waste disposal. This paper presented an overview on the researches about anaerobic digestion of food waste. Technologies (e.g., pretreatment, co-digestion, inhibition and mitigation, anaerobic digestion systems, etc.) were introduced and evaluated on the basis of bibliometric analysis. Results indicated that ethanol and aerobic prefermentation were novel approaches to enhance substrates hydrolysis and methane yield. With the promotion of resource recovery, more attention should be paid to biorefinery technologies which can produce more useful products toward zero emissions. Furthermore, a technological route for food waste conversion based on anaerobic digestion was proposed.

Advanced treatment of wet-spun acrylic fiber manufacturing wastewater using three-dimensional electrochemical oxidation

A three-dimensional electrochemical oxidation (3D-EC) reactor with introduction of activated carbon (AC) as particle micro-electrodes was applied for the advanced treatment of secondary wastewater effluent of a wet-spun acrylic fiber manufacturing plant. Under the optimized conditions (current density of 500A/m2, circulation rate of 5mL/min, AC dosage of 50g, and chloride concentration of 1.0g/L), the average removal efficiencies of chemical oxygen demand (CODcr), NH3-N, total organic carbon (TOC), and ultraviolet absorption at 254nm (UV254) of the 3D-EC reactor were 64.5%, 60.8%, 46.4%, and 64.8%, respectively; while the corresponding effluent concentrations of CODcr, NH3-N, TOC, and UV254 were 76.6, 20.1, and 42.5mg/L, and 0.08Abs/cm, respectively. The effluent concentration of CODcr was less than 100mg/L, which showed that the treated wastewater satisfied the demand of the integrated wastewater discharge standard (GB 8978-1996). The 3D-EC process remarkably improved the treatment efficiencies with synergistic effects for CODcr, NH3-N, TOC, and UV254 during the stable stage of 44.5%, 38.8%, 27.2%, and 10.9%, respectively, as compared with the sum of the efficiencies of a two-dimensional electrochemical oxidation (2D-EC) reactor and an AC adsorption process, which was ascribed to the numerous micro-electrodes of AC in the 3D-EC reactor. Gas chromatography mass spectrometry (GC-MS) analysis revealed that electrochemical treatment did not generate more toxic organics, and it was proved that the increase in acute biotoxicity was caused primarily by the production of free chlorine.

Wastewater-nitrogen removal using polylactic acid/starch as carbon source: Optimization of operating parameters using response surface methodology

Nitrogen removal from ammonium-containing wastewater was conducted using polylactic acid (PLA)/starch blends as carbon source and carrier for functional bacteria. The exclusive and interactive influences of operating parameters (i.e., temperature, pH, stirring rate, and PLA-to-starch ratio (PLA proportion)) on nitrification (Y1), denitrification (Y2), and COD release rates (Y3) were investigated through response surface methodology. Experimental results indicated that nitrogen removal could be successfully achieved in the PLA/starch blends through simultaneous nitrification and denitrification. The carbon release rate of the blends was controllable. The sensitivity of Y1, Y2, and Y3 to different operating parameters also differed. The sequence for each response was as follows: for Y1, pH>stirring rate>PLA proportion>temperature; for Y2, pH>PLA proportion>temperature> stirring rate; and for Y3, stirring rate>pH>PLA proportion>temperature. In this study, the following optimum conditions were observed: temperature, 32.0°C; pH 7.7; stirring rate, 200.0 r ∙min–1; and PLA proportion, 0.4. Under these conditions, Y1, Y2, and Y3 were 134.0 μg-N∙gblend–1∙h–1, 160.9 μg-N∙g-blend–1∙h–1, and 7.6 × 103 μg-O∙g-blend–1∙h–1, respectively. These results suggested that the PLA/starch blends may be an ideal packing material for nitrogen removal.Graphical abstract

Ethanol prefermentation of food waste in sequencing batch methane fermentation for improved buffering capacity and microbial community analysis

This study investigates the effects of ethanol prefermentation (EP) on methane fermentation. Yeast was added to the substrate for EP in the sequencing batch methane fermentation of food waste. An Illumina MiSeq high-throughput sequencing system was used to analyze changes in the microbial community. Methane production in the EP group (254mL/g VS) was higher than in the control group (35mL/g VS) because EP not only increased the buffering capacity of the system, but also increased hydrolytic acidification. More carbon source was converted to ethanol in the EP group than in the control group, and neutral ethanol could be converted continuously to acetic acid, which promoted the growth of Methanobacterium and Methanosarcina. As a result, the relative abundance of methane-producing bacteria was significantly higher than that of the control group. Kinetic modeling indicated that the EP group had a higher hydrolysis efficiency and shorter lag phase.

Effects of digestate recirculation on a two-stage anaerobic digestion system, particularly focusing on metabolite correlation analysis

Single-stage (S-N treatment) and two-stage anaerobic digestion with (T-R treatment) and without digestate recirculation (T-N treatment) for methane production using food waste (FW) were comparatively evaluated to examine the effects of digestate recirculation on anaerobic digestion (AD). Digestate recirculation positively affected the methane yield and organic loading rate (OLR). Metabolite correlation analysis revealed that a systematic hydrolysis degree of greater than 75% is crucial to achieve the complete recoverable yield of methane from FW. Digestate recirculation also markedly increased the system alkalinity, maintaining an optimum pH for methanogens. However, the ammonium accumulated by T-R treatment would destroy the metabolic balance between the hydrolytic bacteria and methanogens, especially at a critical OLR. Therefore, the appropriate control of two-stage AD systems with digestate recirculation is limited not only to OLR regulation but also to the prevention of ammonium accumulation.

Responses of ammonia-oxidizing bacteria community composition to temporal changes in physicochemical parameters during food waste composting

Chemoautotrophic ammonia-oxidizing bacteria (AOB) serve an important function in ecological nitrogen transformation because of their great potential to alleviate ammonia emissions during aerobic composting. However, studies on the influence of specific environmental factors on AOB community dynamics in the food waste composting field are scarce. Hence, this study aimed to identify and prioritize some environmental parameters that affect AOB community composition during food waste composting. The composition and diversity of the AOB community were determined using polymerase chain reaction–denaturing gradient gel electrophoresis (PCR–DGGE). Relationships between the obtained parameters and AOB community composition were simultaneously evaluated by multivariate analysis. Phylogenetic analysis indicated that large amounts of Nitrosomonas-like and Nitrosospira-like lineages existed in different periods. The Nitrosomonas europaea/eutropha were the most dominant AOB species in the thermophilic stage. Redundancy analysis revealed that the dynamics of the AOB community was mainly attributed to temporal changes in nitrate and the pH of the compost material (p < 0.05). Variations (54.7% for AOB species data) were statistically explained by nitrate and pH, suggesting that these parameters were the most likely to influence, or be influenced by AOB community composition, and may further influence nitrogen cycle in the food waste composting ecosystem.

Lactic acid production from Sophora flavescens residues pretreated with sodium hydroxide: Reutilization of the pretreated liquor during fermentation

The feasibility of lactic acid production from Sophora flavescens residues (SFRs) pretreated with sodium hydroxide with the reutilization of the pretreated liquor during fermentation was investigated. After sodium hydroxide pretreatment, 67.5% of the lignin was removed, and hydrolysis efficiency increased from 37.3% to 79.2%. The reutilization of pretreated liquor at 50% loading during open fermentation of unwashed SFR increased lactic acid production by 34.1%. The pretreated liquor acted as pH buffer and resulted in stable pH and high cellulase activity during fermentation. Inhibitors in the pretreated liquor did not affect the growth of lactic acid bacteria but severely inhibited the growth of ethanol-producing yeast. Consequently, lactic acid production increased and ethanol production was zero at 50% loading. Water consumption during pretreatment and fermentation with 50% pretreated liquor was 1.341L per 100g SFR, which was 67.6% lower than that during fermentation with washed SFR.

Multilevel contact oxidation treatment of brewery wastewater using spiral biological carriers and their nitrogen removal mechanism

In this study, spiral biological carriers were used to treat brewery wastewater in a multilevel contact oxidation process. The optimal operational conditions are the following: hydraulic retention time of 6.5 h; temperature of above 21°C; pH of 7.2; and dissolved oxygen concentration ranges of 4.0–6.0 mg/L, 3.0–4.0 mg/L, 2.0–3.0 mg/L, and 2.0–3.0 mg/L in four contact oxidation tanks, respectively. Under the optimal conditions, the removal efficiencies of total nitrogen, ammonia, and CODcr of the system were 77.0%, 87.6%, and 92.2% respectively. Effluent quality met the discharge standard of pollutants for the beer industry (GB 19821–2005). In addition, the aerobic-anoxic micro-and macro-environments were formed in the spiral biological carriers. This could be explained by the specific surface character and three-dimensional spiral structure of these carriers which strengthened the simultaneous nitrification and denitrification (SND) process. The removal efficiency of total nitrogen of the reactor was up t...

Stimulation of methane yield rate from food waste by aerobic pre-treatment

Aerobic pre-treatment (AP) was applied to enhance methane yield from food waste through anaerobic digestion. Different AP durations (i.e. 2, 5 and 8 days) prior to anaerobic digestion were tested. The results indicated that AP of food waste led to no significant differences (p > 0.05) in methane yield potential (ca. 418 mL/g-VS). However, a suitable AP duration (5 days) increased methane yield rates (ca. 18 mL/d/g-VS; 22.0% higher than the control) by anticipating methane generation and shortening the methanogenic phase via volatile fatty acid reduction and pH increase. Although AP induced chemical oxygen demand loss to some extent (i.e. by 2.6%-9.9%) in the AP stage via aerobic degradation, the methane yield potential could be recovered by enhancing organic matter hydrolysis. Therefore, maximisation of hydrolysis should be used as a basis for determining a suitable AP duration for various types of organic matter.

Pilot-scale experiments on multilevel contact oxidation treatment of poultry farm wastewater using saran lock carriers under different operation model

A pilot-scale multilevel contact oxidation reactors system, coupled with saran lock carriers, was applied for the treatment of poultry farm wastewater. The removal efficiencies of CODcr, ammonia, and the total nitrogen as well as the elimination performance of CODcr and total nitrogen along the three-level contact oxidation tanks under six designed operational models were investigated. Based on the performance of the nitrogen removal of the saran lock carriers and the distribution of anoxic-aerobic interspace under the suitable operation model, the mechanism of nitrogen removal of the system was also explored. The results revealed that the intermittent aeration under parallel model is the most suitable operation model, while the removal efficiencies of CODcr, ammonia, and the total nitrogen were 86.86%, 84.04%, and 80.96%, respectively. The effluent concentration of CODcr, ammonia, and the total nitrogen were 55.6 mg/L, 8.3 mg/L, and 12.0 mg/L, which satisfy both the discharge standard of pollutants for livestock and poultry breeding industry (GB 18596-2001) and the first grade of the integrated wastewater discharge standard (GB 8978-1996). Moreover, the mechanism for the nitrogen removal should be attributed to the plenty of anoxic-aerobic interspaces of the biofilm and the three-dimensional spiral structure of the saran lock carriers, where the oxygen-deficient distribution was suitable for the happening of the simultaneous nitrification and denitrification process. Therefore, the multilevel contact oxidation tanks system is an effective pathway for the treatment of the poultry farm wastewater on the strength of a suitable operation model and novel carriers.