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● Decentralized composting (DC) is a profitable KW treating technology. ● SAC and BEC were economically attractive in rural area, while HDC was unprofitable. ● KW handling subsidy plays a vital role in making DC profitable. ● SAC and BEC have great potential in promoting rural KW treatment. This study was designed to evaluate whether the decentralized rural kitchen waste (KW) composting technologies used in China can be widely applied. To this end, we completed a techno-economic analysis of three typical types of KW compositing, namely solar-assisted (SAC), bio-enhanced (BEC), and heat-dewatering composting (HDC). These evaluations revealed that all three technologies produce composting products that meet China’s organic fertilizer standard and that both SAC and BEC are economically self-sustaining and generate net profits (18824.94 and 17791.52 US$/a) and positive net present values (32133.11 and 25035.93 US$). Subsequent sensitivity analysis demonstrated that the KW-handling subsidy plays a critical role in making decentralized composting economically attractive. Based on these analyses, we believe that reducing the coverage area of SAC, reducing the operating cost of BEC and HDC, upgrading composting products, and strengthening secondary pollution control would aid in supporting the technological improvement of these processes. Moreover, providing appropriate subsidies and promulgating specific standards and policies for KW fertilizer are key strategies for decentralized rural KW composting management.

1-Butanol (1-BD) is a promising fuel additive which can be biosynthesized via reversed β-oxidation pathway in bacteria. However, heterologous reversed β-oxidation pathway is a carbon chain prolongation process with several genes overexpressed in most of bacterial hosts, leading to low titer of 1-BD and high cost for production. Here we displayed a forward β-oxidation pathway for 1-BD production in a kitchen waste oil (KWO) degrading Pseudomonas aeruginosa PA-3, and we proved that aldehyde dehydrogenase (ALDH) is a checkpoint for diverting metabolic flux into 1-BD biosynthesis. With nitrogen source supplied, titer of 1-BD was increased accompanied with 12 ALDH coding genes transcriptionally promoted to different degrees. At the same time, binding energies of these ALDHs with different length of acyl-CoAs in β-oxidation were calculated to identify their specificities. Based on the above information, ALDH deletions were conducted. We certified that deletion of ALDH8 and ALDH9 led to significant decreased titers of 1-BD. Finally, these two ALDHs were separately overexpressed in PA-3, and titer of 1-BD was promoted to 1.36 g/L at 72 h in shake flask. Totally in this work, we provided a forward β-oxidation pathway for 1-BD production from KWO, and the roles of ALDHs were confirmed.

Households, restaurants, canteens, and hotel wastes constitute kitchen waste. Every day our growing cities generate more and more waste, which is overloading our municipal systems. The main aim of the present work was to prepare a microbial consortium that can effectively and rapidly bring about the degradation of kitchen wastes that can be used in agricultural soils. More than 100 different bacterial isolates were obtained from various kitchen waste dumping areas. The bacterial isolates were studied to produce enzymes like amylase, gelatinase, lipase, and protease on respective media plates. The best 20 isolates were subjected to enzyme quantification. The isolates showing maximum production for all four enzymes were selected for consortia preparation. The consortia of isolates were prepared by permutation combinations. Amongst all consortia prepared consortium No. 7 showed maximum enzymatic potential. The bacterial isolates in the best consortium (No. 7) were further characterized and identified as KW104 Serratia marcescens, KW37 Micrococcus luteus, KW128 Brevindimonas mediterranea, KW91 Bacillus tequilensis, and KW97 Exiguobacterium mexicanum. This consortium showed rapid degradation of waste as compared to others in 15 days duration of time showing good potential for compost formation when applied to plant growth.

Biodiesel from insect larvae is an alternative to plant biodiesel, which have issues of using edible plants. On the contrary, insects can grow on waste. Although the conversion of larval lipids to biodiesel is known, characterisation of larval biodiesel is rarely reported. Here, black soldier fly larvae were cultivated for 20 days on kitchen waste. Larval lipids were extracted and converted to biodiesel by two-step transesterification. Analysis by optical polarisation microscopy from − 5 to + 15 °C showed tiny needle-like shaped crystals. Fourier transform infrared spectra of black soldier fly biodiesel revealed absorption bands at 1459 and 1435 cm−1 corresponding to methyl ester, the main functional group of biodiesel. Nuclear magnetic resonance (NMR) analysis confirmed the presence of methyl ester by showing peaks at 3.6 and 2.3 ppm by 1H NMR, and at 176 and 51.56 ppm by 13C NMR. Overall, our results confirm the successful conversion of black soldier fly larval lipid to biodiesel. This biodiesel met the American Society for Test and Materials D6751 and European Standard 14214.

In this article a significant improvement for the chemical analytic is presented to overcome the gap of a fast and accurate carbohydrate measurement during anaerobic digestion. The new method is an easily manageable and accurate carbohydrate analysis for solutions which are difficult to analyse, such as mixtures of substrate with anaerobic sludge. The method can be used for soluble carbohydrate measurements for particles ø ≤ 0.45 μ m . Additionally, solutions with insoluble carbohydrates or larger particles were successfully hydrolysed and then measured. Hydrolysing a viscose model kitchen waste solution with a carbohydrate content in the range between 5.3 and 42.5 gL - 1 led to complete recovery with a relative derivation of less than ± 4%. This new method is accurate, inexpensive and safe. The advantages and features are presented and offers the possibility of carbohydrate degradation monitoring during anaerobic digestion. Graphical Abstract

This study aimed to evaluate the effects of fermentation products of kitchen waste (FPKW) on growth, apparent digestibility, digestive enzyme activities, and serum biochemistry for juvenile allogynogenetic gibel carp “CAS III.” A total of 540 fish (7.47 ± 0.20 g/fish) were distributed among 18 aquariums at a density of 30 fish per tank in a completely randomized design (triplicated) and were fed diets containing 0, 6, 9, 12, 15, and 30% FPKW for 60 days. The results showed the weight gain rate (WGR) of fish varied quadratically with FPKW, and the WGRmax was observed when FPKW supplementation was 11.13%. Compared to the control group, the protease and lipase activities in midgut and hepatopancreas increased significantly when FPKW was 12%. The apparent digestibility of dry matter and crude protein in 30% FPKW group were significantly lower than other groups. The levels of total cholesterol, triglycerides, alkaline phosphatase, aspartate aminotransferase, and alanine aminotransferase in serum were significantly higher than other groups when FPKW was 30%. The histological examination of hepatopancreas, midgut, and kidney of fish was consistent with the growth and digestive capacity. In conclusion, there were positive effects on fish when FPKW was less than 12%.

Kitchen waste hydrolysis residue (KWHR), which is produced in the bioproduction process from kitchen waste (KW), is usually wasted with potential threats to the environment. Herein, experiments were carried out to evaluate the potential of KWHR as adsorbent for dye (methylene blue, MB) removal from aqueous solution. The adsorbent was characterized using FT-IR and SEM. Adsorption results showed that the operating variables had great effects on the removal efficiency of MB. Kinetic study indicated pseudo-second-order model was suitable to describe the adsorption process. Afterwards, the equilibrium data were well fitted by using Langmuir isotherm model, suggesting a monolayer adsorption. The Langmuir monolayer adsorption capacity was calculated to be 110.13 mg/g, a level comparable to some other low-cost adsorbents. It was found that the adsorption process of MB onto KWHR was spontaneous and exothermic through the estimation of thermodynamic parameters. Thus, KWHR was of great potential to be an alternative adsorbent material to improve the utilization efficiency of bioresource (KW) and lower the cost of adsorbent for color treatment.

Due to the scarcity of resources, alternatives to non-renewable resources have become more important. Chemical catalysts react violently and the conditions are harsh. Using biocatalysts at the water/oil (W/O) interface remains technically challenging and is rewarding. In this study, the Thermomyces lanuginosus lipase-poly coupling biocatalyst was prepared by the atom transfer radical polymerization “grafting-from” method. The TL–PNIPAAm conjugate was successfully prepared and circular dichroism showed a negligible change between the free enzyme and conjugated enzyme by sodium dodecyl sulfate–polyacrylamide gel electrophoresis and transmission electron microscopy. Furthermore, the temperature and pH stability of the conjugate was better than that of free TL. The remaining activity of the TL–PNIPAAm conjugate for 10 h was approximately 20% higher than that of free TL after heat treatment (55 °C) and higher pH stability was obtained in the pH 4–10. The remaining activity of the TL–PNIPAAm conjugates was above 60% after recycling 7 times. In addition, the conversion of biodiesel from kitchen waste oil was 92.6% at 50 °C for 25 h with a conversion efficiency of 0.04 g/mL/h. Thus, a high stability and reusability biocatalyst and stabilizer at the interface of water-in-oil Pickering emulsions was successfully prepared. Graphical Abstract

In this study, an anaerobically digested effluent from kitchen waste with high concentrations of chemical oxygen demand (COD) and ammonia nitrogen was treated using combined processes of anaerobic digestion (AD), complete nitritation (CN), and anaerobic ammonium oxidation (ANAMMOX). The COD and nitrogen removal efficiency of each treatment unit were investigated. The feasibility of using the final treatment effluent to dilute the original wastewater was also discussed. Findings showed that as a pretreatment step, AD resulted in the decline in biodegradability and increase in NH 4 + − N concentration. CN was successfully and stably achieved for 106 days with an average nitritation rate of 95% by maintaining the dissolved oxygen at 2–3 mg/L and hydraulic retention time of 24 hr under 30 ± 1°C. High NH 4 + − N and NO 2 − − N . removal efficiencies of over 88% and 96% were attained in the following ANAMMOX reactor. The reflux of ANAMMOX-treated effluent for the dilution of raw wastewater or an influent of CN and ANAMMOX ensured the stable operation of the combined system. • Practitioner points • Anaerobic digestion effluent of kitchen waste had low COD/ NH 4 + − N ratio and poor biodegradability. • Stable and efficient nitritation was realized by controlling DO, HRT and TEMP. • High NH 4 + − N and NO 2 − − N removal efficiency were obtained by ANAMMOX process. • Average nitrogen removal rate of 0.94 kg N/m³/day were obtained by ANAMMOX. • Reflux dilution with the effluent guaranteed the system’s successful operation.

This study presents sustainable succinic acid production from the organic fraction of household kitchen wastes, i.e., the organic fraction of household kitchen waste (OFHKW), pretreated with enzymatic hydrolysis (100% cocktail dosage: 62.5% Cellic® CTec2, 31%% β-Glucanase and 6.5% Cellic ® HTec2, cellulase activity of 12.5 FPU/g-glucan). For fermentation, A. succinogenes was used, which consumes CO2 during the process. OFHKW at biomass loading > 20% (dry matter) resulted in a final concentration of fermentable sugars 81–85 g/L and can be treated as a promising feedstock for succinic production. Obtained results state that simultaneous addition of gaseous CO2 and MgCO3 (>20 g/dm3) resulted in the highest sugar conversion (79–81%) and succinic yields (74–75%). Additionally, CH4 content in biogas, used as a CO2 source, increased by 21–22% and reached 91–92% vol. Liquid fraction of source-separated kitchen biowaste and the residue after succinic fermentation were successfully converted into biogas. Results obtained in this study clearly document the possibility of integrated valuable compounds (succinic acid) and energy (biogas) production from the organic fraction of household kitchen wastes (OFHKW).