Adjusting Organic Load as a Strategy to Direct Single-Stage Food Waste Fermentation from Anaerobic Digestion to Chain Elongation

Production of medium chain carboxylic acids (MCCA) as renewable feedstock bio-chemicals, from food waste (FW), requires complicated reactor configurations and supplementation of chemicals to achieve product selectivity. This study evaluated the manipulation of organic loading rate in an un-supplemented, single stage stirred tank reactor to steer an anaerobic digestion (AD) microbiome towards acidogenic fermentation (AF), and thence to chain elongation. Increasing substrate availability by switching to a FW feedstock with a higher COD stimulated chain elongation. The MCCA species n-caproic (10.1 ± 1.7 g L−1) and n-caprylic (2.9 ± 0.8 g L−1) acid were produced at concentrations comparable to more complex reactor set-ups. As a result, of the adjusted operating strategy, a more specialised microbiome developed containing several MCCA-producing bacteria, lactic acid-producing Olsenella spp. and hydrogenotrophic methanogens. By contrast, in an AD reactor that was operated in parallel to produce biogas, the retention times had to be doubled when fed with the high-COD FW to maintain biogas production. The AD microbiome comprised a diverse mixture of hydrolytic and acidogenic bacteria, and acetoclastic methanogens. The results suggest that manipulation of organic loading rate and food-to-microorganism ratio may be used as an operating strategy to direct an AD microbiome towards AF, and to stimulate chain elongation in FW fermentation, using a simple, un-supplemented stirred tank set-up. This outcome provides the opportunity to repurpose existing AD assets operating on food waste for biogas production, to produce potentially higher value MCCA products, via simple manipulation of the feeding strategy.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 66599

Selecting fermentation products for food waste valorisation with HRT and OLR as the key operational parameters.

Acidogenic fermentation is attractive for food waste valorisation. A better understanding is required on how operation affects product selectivity. This study demonstrated that the hydraulic retention time (HRT) and organic loading rate (OLR) selected fermentation pathways in a single-stage, semicontinuous stirred tank reactor. Three combinations of HRT and OLR were tested to distinguish the effect of each parameter. Three fermentation profiles with distinct microbial communities were obtained. Predominantly n-butyric acid (13 ± 2 gCOD L-1, 55 ± 14% of carboxylates) was produced at an HRT of 8.5 days and OLR around 12 gCOD L-1 d-1. Operating at an HRT two days longer, yet with similar OLR, stimulated chain elongation (up to 13.6 gCOD L-1 of n-caproic acid). This was reflected by a microbial community twice as diverse at longer HRT as indicated by first and second order Hill number (1D = 24 ± 4, 2D = 12 ± 3) and by a higher relative abundance of genera related to secondary fermentation, such as the VFA-elongating Caproiciproducens spp., and secondary lactic acid fermenter Secundilactobacillus spp.. Operating at a higher OLR (20 gCOD L-1 d-1) but HRT of 8.5 days, resulted in typical lactic acid fermentation (34 ± 5 gCOD L-1) harbouring a less diverse community (1D = 8.0 ± 0.7, 2D = 5.7 ± 0.9) rich in acid-resistant homofermentative Lactobacillus spp. These findings demonstrate that a flexible product portfolio can be achieved by small adjustments in two key operating conditions. This improves the economic potential of acidogenic fermentation for food waste valorisation

Application of membrane bioreactor technology for urban wastewater treatment in Tunisia:Focus on treated water quality

Water is a fundamental issue for the current and future development of Tunisia. In fact, effective water management is essential for socio-economic development and for maintaining healthy ecosystems. The balance between available water resources and the need for water supply is growing from one year to another, and the deficit in water resources is rapidly becoming larger. To fill in this gap, a strategy based on water conservation and the search of unconventional resources, such as reuse of treated wastewater, has been adopted in Tunisia. Membrane technology can make a significant contribution since membrane filtration enables the production of high quality water. The paper summarizes results of the EC-funded PURATREAT project (Contract No. 015449) and aims to assess the efficiency of submerged membrane bioreactor (SMBR) technology in domestic wastewater treatment with a view to reuse. A treated water of a high physicochemical and microbiological quality was obtained after treatment, such that the water could be reused for unrestricted irrigation of ground crops for human consumption

Modelling energy consumption in membrane bioreactors for waste water treatment in North Africa

Two pilot-scale membrane bioreactors were operated alongside a full-sized activated sludge plant in Tunisia in order to compare specific energy demand and treated water quality. Energy consumption rates were measured for the complete membrane bioreactor systems and for their different components. Specific energy demand was measured for the systems and compared with the activated sludge plant, which operated at around 3 kWh m(-3). A model was developed for each membrane bioreactor based on both dynamic and steady-state mass balances, microbial kinetics and stoichiometry, and energy balance. Energy consumption was evaluated as a function of mixed-liquor suspended solids concentration, net permeate fluxes, and the resultant treated water quality. This work demonstrates the potential for using membrane bioreactors in decentralised domestic water treatment in North Africa, at energy consumption levels similar or lower than conventional activated sludge systems, with the added benefit of producing treated water suitable for unrestricted crop irrigation

Multi-residue ultra-performance liquid chromatography coupled with tandem mass spectrometry method for comprehensive multi-class anthropogenic compounds of emerging concern analysis in a catchment-based exposure-driven study.

This paper presents a new multi-residue method for the quantification of more than 142 anthropogenic compounds of emerging concern (CECs) in various environmental matrices. These CECs are from a wide range of major classes including pharmaceuticals, household, industrial and agricultural. This method utilises ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS) for analysis of five matrices (three liquid and two solid) from wastewater treatment processes and the surrounding environment. Relative recoveries were predominantly between 80 and 120%; however, due to the complexity of the matrices used in this work, not all compounds were recovered in all matrices, from 138/142 analytes in surface water to 96/142 analytes in digested solids. Method quantification limits (MQLs) ranged from 0.004 ng L−1 (bisoprolol in surface water) to 3118 ng L−1 (creatinine in wastewater treatment work (WwTW) influent). The overall method accuracy was 107.0%, and precision was 13.4%. To test its performance, the method was applied to the range of environmental matrices at WwTWs in South West England. Overall, this method was found to be suitable for application in catchment-based exposure-driven studies, as, of the total number of analytes quantifiable in each matrix, 61% on average was found to be above their corresponding MQL. The results confirm the need for analysing both the liquid and solid compartments within a WwTW to prevent under-reporting of concentrations

New aminocyclitols with quaternary stereocentres via acylnitroso cycloaddition with an<em> ipso,ortho</em>-arene dihydrodiol

AbstractMicrobial ipso,ortho-dihydroxylation of benzoic acid by the B9 mutant strain of Ralstonia eutropha permits rapid construction of aminocyclitols containing a quaternary stereocentre. Installation of the amine functionality is achieved by use of an acylnitroso dienophile for a hetero-Diels–Alder reaction. Both aminotetrols and aminohexols are accessible as single enantiomers by this route. Both NOESY spectroscopic and X-ray crystallographic analyses were required to distinguish cycloadduct isomers. Notably, subsequent to the biooxidation step, all new stereocentres are installed under substrate control. Thus, all stereochemical information is ultimately of enzymatic origin