RETRACTED: Effect of the solid retention time in the obtention of polyhydroxyalkanoates [version 1; peer review: awaiting peer review]

At the request of the authors, the article titled "Effect of the solid retention time in the obtention of polyhydroxyalkanoates" [version 1; peer review: awaiting peer review]. F1000Research 2021, 10:864 (https://doi.org/10.12688/f1000research.28852.1) has been retracted from F1000Research. Since publication of the article, the corresponding author has notified the Editorial team that this work was originally performed at University of A Coruña with the involvement of María C. Veiga and Christian Kennes, who were not notified regarding the submission of this manuscript or listed as authors. After discussion with all parties, including contact with the corresponding author’s institution, it was agreed that the article would be retracted in order to correct the academic record. As the article contains content which potentially should not have been made publicly available the content of the article has been removed. The authors apologise for this honest error.

The Future Challenges of Anaerobic Membrane Bioreactor (AnMBR) for High Strength Wastewater

This article is to present a review of anaerobic membrane bioreactor (AnMBR), process, operational condition, fouling mechanism and future challenge for high strength wastewater. Since1969s, membrane filtration technology has been used and continuously developed for wastewater treatment and recovery. AnMBR has proposed for the economic feasibility owing to the low footprint, high yield production under the relatively low energy consumption. Continuous stirred tank reactor (CSTR) configuration is the widely used couple with a flat sheet or hollow fibre modules. The various factors of operating condition are influence on the performance such as hydraulic retention time (HRT= 6 – 12 d), solid retention time (SRT > 100 d) and operating temperature (T = 10 - 56oC). In addition, the increase in temperature is related to high methanogenic activity and high COD removal efficiency (85% - 99%). However, the limitation of this process is fouling that occurs from the soluble microbial product (SMP), exopolymer substance (EPS) and biopolymer cluster (BPC). Almost of appropriate operating conditions for high performance, anti-fouling, the majority of effective microorganisms and energy balance are discussed in detail. For the challenge work, improvement of the prevention membrane fouling and high energy recovery in the hybrid/combination system with forward osmosis (FO), membrane distillation (MD) and powder activated carbon (PAC)-AnMBR.

Effect of the solid retention time in the obtention of polyhydroxyalkanoates

Background: The effect of solid retention time (SRT) over cheese whey substrates in a fermentation process drives changes in the composition of polyhydroxyalkanoates (PHAs) obtained. Volatile fatty acids produced in the first step of an anaerobic sequencing batch reactor were used as substrates to produce PHA using mixed microbial cultures under aerobic dynamic feeding conditions. Methods: Analytical methods were used for the standard analysis of parameters of interest including measuring the amount of ammonium and phosphate, chemical oxygen demand, among others. Results: The SRT increasing from 4 to 6 and 10 days produced changes in the distribution of volatile fatty acids produced. The polyhydroxybutyrate-hydroxyvalerate copolymers formed in the accumulation stage gave the following results: 58:42, 68:32 and 81:19 (%), referred to SRTs of 10, 6 and 4 days, respectively. The maximum PHA accumulation obtained at 10 days of SRT was 52% of the dry cell weight within 7 h, reaching a PHA productivity of 0.62 g L−1 h−1 and a storage yield of 0.37. Conclusion: The SRT variation impact on the distribution of volatile fatty acids in the acidogenic reactor and consequently on the PHA production and composition formed in the accumulation stage.

Machine Learning Approach Reveals the Assembly of Activated Sludge Microbiome with Different Carbon Sources during Microcosm Startup

Activated sludge (AS) microcosm experiments usually begin with inoculating a bioreactor with an AS mixed culture. During the bioreactor startup, AS communities undergo, to some extent, a distortion in their characteristics (e.g., loss of diversity). This work aimed to provide a predictive understanding of the dynamic changes in the community structure and diversity occurring during aerobic AS microcosm startups. AS microcosms were developed using three frequently used carbon sources: acetate (A), glucose (G), and starch (S), respectively. A mathematical modeling approach quantitatively determined that 1.7–2.4 times the solid retention time (SRT) was minimally required for the microcosm startups, during which substantial divergences in the community biomass and diversity (33–45% reduction in species richness and diversity) were observed. A machine learning modeling application using AS microbiome data could successfully (>95% accuracy) predict the assembly pattern of aerobic AS microcosm communities responsive to each carbon source. A feature importance analysis pinpointed specific taxa that were highly indicative of a microcosm feed source (A, G, or S) and significantly contributed for the ML-based predictive classification. The results of this study have important implications on the interpretation and validity of microcosm experiments using AS.

Optimization of In-situ Transesterification Process for Biodiesel Production from High Free Fatty Acid Feedstock by Semi-continuous Column Reactor

An in-situ transesterification (in-situ TE) process can reduce the multiple steps of biodiesel production by merging vegetable oil extraction and biodiesel synthesis into a single step. However, high free fatty acid, generally found in waste feedstock, dramatically reduce both yield and quality of biodiesel. In this work the new concept of a semi-continuous column reactor was introduced to mitigate the negative effect of high free fatty acid found in spent coffee grounds (SCGs). The potassium methoxide solution, as reactive solvent, was pumped through the series of column reactors. At the beginning of process free fatty acid in SCGs was promptly extracted in form of soap as a pretreatment fraction. Then, the residual mono-, di- and triglyceride in SCGs matrix were covert to fatty acid methyl ester (FAME) biodiesel and simultaneously extracted. A liquid fraction analysis was conducted to distinguish the pretreatment fraction from biodiesel. A central composited rotatable design was applied to determine optimal process conditions of potassium methoxide concentration and solid retention time at 30°C. Under the optimal conditions, up to 88% FAME yield was observed. The residual triglyceride in defatted SCGs was less than 1.5%mass. Compared to batch reactor type, the semi-continuous column reactor used only half of the required methanol for in-situ TE by recirculating the reagent in the series of reactors. This could dramatically reduce the energy usage and environmental impact of FAME production from high free fatty acid feedstock via in-situ TE.

Effect Of Hydrothermal Pre-Treatment On Methane Production During Anaerobic Digestion Of Thickened Waste Activated Sludge

The effects of hydrothermal pre-treatment on the production of methane and biogas on thickened waste activated sludge was investigated. This paper reviews the anaerobic digestion process and its complexities, provides an overview of the different stages of the anaerobic digestion process, different kinds of feedstocks and the essential and influential operating parameters such as temperature, pH, organic loading rate, solid retention time and particle size. This paper also demonstrates an overview of the natural and anthropogenic sources contributing to methane in the atmosphere. It further provides a recommendation on essential practices and methods required to enhance methane capture in the atmosphere. Furthermore, an experimental setup consisting of batch anaerobic digestion was employed for the sample analysis the purpose of this experimental research was to conduct a comprehensive assessment of the effect of the hydrothermal pre-treatment on thickened waste activated sludge and to determine the most optimum conditions to produce methane. Keywords: Anaerobic digestion, Thickened waste-activated sludge, Hydrothermal Pre-treatment

Modeling Of Dark Fermentation Process For Volatile Fatty Acids Production

This study examined the fermentation process for the production of volatile fatty acids from the organic waste. The depletion of fossil fuels motivated researchers to search for alternative energy and fuels instead of relying on the non-renewable way of energy and fuel production. Anaerobic digestion is a biochemical process in the absence of oxygen, where complex organic matter are degraded. The different stages of anaerobic digestion and important operating parameters such as pH, temperature and retention time. The most suitable feedstock and its effects on the treatment process are discussed. This study evaluates the modelling of VFAs production. The paper also demonstrates various model like ADM1, surface limiting model, and steady-state model. Furthermore, an experimental setup consisting of two semi-continuous reactors was employed for the sample analysis. The reactors were fed with raw and pre-treated source separated organics with solid retention time of 3 days. Keywords: Anaerobic digestion, Feedstocks, SSO, VFAs, ADM1

Modeling Of Dark Fermentation Process For Volatile Fatty Acids Production

This study examined the fermentation process for the production of volatile fatty acids from the organic waste. The depletion of fossil fuels motivated researchers to search for alternative energy and fuels instead of relying on the non-renewable way of energy and fuel production. Anaerobic digestion is a biochemical process in the absence of oxygen, where complex organic matter are degraded. The different stages of anaerobic digestion and important operating parameters such as pH, temperature and retention time. The most suitable feedstock and its effects on the treatment process are discussed. This study evaluates the modelling of VFAs production. The paper also demonstrates various model like ADM1, surface limiting model, and steady-state model. Furthermore, an experimental setup consisting of two semi-continuous reactors was employed for the sample analysis. The reactors were fed with raw and pre-treated source separated organics with solid retention time of 3 days. Keywords: Anaerobic digestion, Feedstocks, SSO, VFAs, ADM1