The anaerobic digestion of biologically and physicochemically pretreated oily wastewater

New insight into the metabolic mechanism of a novel lipid-utilizing and denitrifying bacterium capable of simultaneous removal of nitrogen and grease through transcriptome analysis

Introduction

Issues related to fat, oil, and grease from kitchen waste (KFOG) in lipid-containing wastewater are intensifying globally. We reported a novel denitrifying bacterium Pseudomonas CYCN-C with lipid-utilizing activity and high nitrogen-removal efficiency. The aim of the present study was aim to explore the metabolic mechanism of the simultaneous lipid-utilizing and denitrifying bacterium CYCN-C at transcriptome level.

Methods

We comparatively investigated the cell-growth and nitrogen-removal performances of newly reported Pseudomonas glycinae CYCN-C under defined cultivation conditions. Transcriptome analysis was further used to investigate all pathway genes involved in nitrogen metabolism, lipid degradation and utilization, and cell growth at mRNA levels.

Results

CYCN-C could directly use fat, oil, and grease from kitchen waste (KFOG) as carbon source with TN removal efficiency of 73.5%, significantly higher than that (60.9%) with sodium acetate. The change levels of genes under defined KFOG and sodium acetate were analyzed by transcriptome sequencing. Results showed that genes cyo, CsrA, PHAs, and FumC involved in carbon metabolism under KFOG were significantly upregulated by 6.9, 0.7, 26.0, and 19.0-folds, respectively. The genes lipA, lipB, glpD, and glpK of lipid metabolic pathway were upregulated by 0.6, 0.4, 21.5, and 1.3-folds, respectively. KFOG also improved the denitrification efficiency by inducing the expression of the genes nar, nirB, nirD, and norR of denitrification pathways.

Conclusion

In summary, this work firstly provides valuable insights into the genes expression of lipid-utilizing and denitrifying bacterium, and provides a new approach for sewage treatment with reuse of KFOG wastes.

Evaluate the effectiveness technology for the treatment of oily wastewater

This work deals with the treatment of oily wastewater produced from the washing of oil-contaminated soil. Untreated oily wastewater contains toxic compounds that might be mutagenic or carcinogenic as total petroleum hydrocarbon (TPH) and heavy metals. Based on the water quality analysis, the tested samples contained a high concentration of TPH, chemical oxygen demand (COD) and turbidity with an average value of 67,500 mg/l, 48,240 mg/l and 176 (nephelometric turbidity unit, NTU), respectively. Several technologies were used, such as centrifuging, powdered activated carbon (PAC) and sawdust. The mean values of COD values for sawdust, centrifuging and PAC were 41,067, 25,600 and 13,133 mg/l, respectively. The present study indicated that the coagulation/flocculation processes were more efficient by using aluminium sulphate alum, while the preliminary conclusion derived was that the secondary treatment using an aeration system is capable of lowering the COD values as well as increasing the flocculent mass floc well equal to 4,784 mg/l and 0.69 g, respectively. The microbial seed was able to degrade the biosurfactant, which allows the stability of oil emulsion to be broken down and released easily.

Anaerobic digestion: An alternative resource treatment option for food waste in China

With the implementation of zero-waste city and waste classification in China, a large amount of food waste (FW) began to appear in concentration, and there was an urgent requirement for appropriate and efficient treatment technology. Traditional FW disposal methods (landfill and incineration) could cause several environmental problems, so resource recycling has become the main development trend of FW in China. In recent years, anaerobic digestion (AD) technology for FW resource treatment has attracted much attention due to its advantages such as the ability to obtain clean energy, low carbon emissions, and suitability for large-scale treatment compared with other recycling technologies (composting, feed, and breeding insects). Chinese policy is conducive to the development of AD for FW, which has the potential to produce methane and achieve economic and environmental benefits. This paper presents an overview of the researches, application situations, and perspectives for the AD of FW resource treatment in China. The bibliometric analysis shows that China has the most interest in the AD of FW compared to other countries, and the amount and characteristics analysis of FW indicates that FW is suitable for treatment by AD. At the same time, this review analyzes the influence factors, methods to promote AD, working mechanism, secondary pollution of AD. Besides, the article introduces and analyzes the current policies, application status, economic and environmental benefits, and problems of AD for FW resource treatment in China. AD is considered as an alternative resource treatment technology for FW, although there are still several problems such as odors, digestate, etc. In the future, China should focus on the reform of management policy, the implementation of the AD circular economy model, and the research of the biorefinery model based on AD technology.

First approaches to valorizate fat, oil and grease (FOG) as anaerobic co-substrate with slaughterhouse wastewater: Biomethane potential, settling capacity and microbial dynamics

Anaerobic digestion (AD) is the biological preferred treatment applied to Slaughterhouse wastewaters (SWW) due to its effectiveness. The aim of the study is to investigate the effect of different percentages of fats, oil and grease (FOG) on biomethane production in anaerobic co-digestion with slaughterhouse wastewater using BMP tests under mesophilic conditions (35 °C). For this purpose, three percentages of FOG from 1% to 10% were tested. Biodegradability, biomethane production and the microbial population were studied. In addition, settling capacity has been evaluated at different conditions: i) before and after anaerobic co-digestion; ii) at different temperature 25 °C and 35 °C. The settling rates as well as the characterization of the digestate were recorded. Experimental results showed that all the co-digestion mixtures (FOG percentages = 1-10%) enhanced biomethane production and biodegradability compared to AD of sole SWW. The best conditions were achieved at 5-10% of FOG, showing biodegradability of 66-70% CODt_removal and specific biomethane productions of 562 and 777 mL_CH4·g^-1_CODsremoved, respectively. Regarding microbial dynamics, Eubacteria was reduced with the increase in %FOG but Acetate utilizing methanogens was increased. Regarding settling capacity, mesophilic temperatures (35 °C) increased the settling rate of digestate in 1.76 times and reduced the lag-phase to 0.92 min; obtaining a more concentrated sludge and leaving a clarified whose TSS represent only 8% of TS.

Recent improvements in oily wastewater treatment: Progress, challenges, and future opportunities

Oily wastewater poses significant threats to the soil, water, air and human beings because of the hazardous nature of its oil contents. The objective of this review paper is to highlight the current and recently developed methods for oily wastewater treatment through which contaminants such as oil, fats, grease, and inorganics can be removed for safe applications. These include electrochemical treatment, membrane filtration, biological treatment, hybrid technologies, use of biosurfactants, treatment via vacuum ultraviolet radiation, and destabilization of emulsions through the use of zeolites and other natural minerals. This review encompasses innovative and novel approaches to oily wastewater treatment and provides scientific background for future work that will be aimed at reducing the adverse impact of the discharge of oily wastewater into the environment. The current challenges affecting the optimal performance of oily wastewater treatment methods and opportunities for future research development in this field are also discussed.

Denitrifying sulfide removal and nitrososulfide complex: Azoarcus sp. NSC3 and Pseudomonas sp. CRS1 mix

Denitrifying sulfide removal (DSR) process simultaneously removes nitrate, sulfide and organic matters in the same reactor. This study applied Azoarcus sp. NSC3 and Pseudomonas sp. CRS1 mix for DSR tests in autotrophic, heterotrophic and mixotrophic growths. Negligible NO-compounds were noted in heterotrophic or mixotrophic growths, while most cells were damaged and bound with NO-compounds in autotrophic growth. Nitroprusside (SNP) ions were applied as model compound to reveal the formation of nitrososulfide complex (RSNO) by nitroso (NO(+)) and excess sulfide (S(2-)), rather than the previously proposed mechanism by direct reaction between nitric oxide (NO) and S(2-). We speculated that RSNO was then abiotically decomposed to NO and elemental sulfur in the presence of biological cells. A revised nitrogen cycle considering interactions with sulfur compounds was proposed. We also speculated that SNO and NO were inhibitory to the functional strains, whose efficient removals were essential to reach high-rate DSR performance.