Advances in enhanced volatile fatty acid production from anaerobic fermentation of waste activated sludge.

Municipal solid waste (MSW) management has emerged as probably the most pressing issue many governments nowadays are facing. Traditionally, Waste-to-Energy(WtE) is mostly associated with incineration, but now, with the emergence of the bioeconomy, it embraces a broader definition comprising any processing technique that can generate electricity/heat or produce a waste-derived fuel. Under the ambit of the circular economy many nations are looking for, additional effort must be made to be sure of acquiring the most updated information and paving a sustainable path for managing MSW in such a frame. In this regard, we have undertaken a critical review of various technologies, with their updated progress, involved in the exploitation of MSW as a renewable resource, along with the critical advantages and limitations on energy and material cycling for sustainable MSW management. Incineration, the most widely used method, is nowadays difficult to further apply due to its dubious reputation and social opposition. Meanwhile, to address the organic fraction of MSW which currently is mostly unrecycled and causes disposal issues, the biological approach presents an attractive option. The new emphasis of bioeconomy leads us to understand how environmental biotechnologies should be better connected/integrated for more sustainable MSW management. This article is concluded with advances of future prospects, which can serve as a timely reminder to encourage competent authorities/researchers to work towards further improvement of the present MSW management system.

A critical review: emerging bioeconomy and waste-to-energy technologies for sustainable municipal solid waste management

Many operating parameters, individually or together, may influence the performance of anaerobic digestion towards biogas or digestate yield and quality maximization. The most preferred method of optimizing an anaerobic digestion plant often relies on how carefully the crucial parameters, such as pH, temperature, organic loading rate, hydraulic retention time, and pressure, are chosen. There is a large amount of literature available on optimization of anaerobic digestion; however, given the continued development and implementation of innovative technologies, together with the introduction of increasingly complex systems, it is necessary to update present knowledge on process parameters and their role on operational ranges and flexibilities in real-life anaerobic digestion system. Accordingly, the present review discusses the importance of the selection of operational parameters in existing technologies and their impact on biogas yield. Notably, the four broad areas of feedstock utilization (substrate, inoculum, codigestion and pretreatment), process condition (pH, temperature, pressure, and reactor design), reactor control (HRT and OLR) and inhibition (Ammonia and VFAs) are covered in this review. In addition, particular emphasis is placed on the most recent innovations that have been or may be implemented in current or future biogas plants.

A Review of the Role of Critical Parameters in the Design and Operation of Biogas Production Plants

https://arpi.unipi.it/bitstream/11568/991746/4/Manuscript_rene.pdf

Comparison of single-stage and two-stage anaerobic Co-Digestion of food waste and activated sludge for hydrogen and methane production

Anaerobic co-digestion in thermophilic condition leads to efficient waste treatment and energy recovery through accelerated and enhanced synergism. The performance of anaerobic co-digestion of food waste with chicken manure was investigated for overcoming the challenges due to process inhibition during mono-digestion of food waste. The bench scale anaerobic Continuously Stirred Tank Reactor (CSTR) system with the working volume of 87 L in wet condition with 10% total solids content was used for this study. Though thermophilic food waste anaerobic digestion indicated high methane yield and solids reduction, the process stability was affected at higher loading. Whereas, the reduction in FOS/TAC value (the ratio of volatile fatty acids to total alkalinity) through co-digestion indicated the higher capacity for organic loading rate in the anaerobic co-digestion system due to synergistic effect of microorganisms, buffering capacity and nutrient balance by C/N adjustment in the feedstock. Moreover, the percentage increases of specific methane yields in co-digestion compared with mono-digestion was found to be 33.2%, 10.4%, 12.1% and 89.9% at organic loading rates (OLR) of 1, 2, 3 and 4 kg VS‧m−3‧d−1 respectively, as a consequence of the improvement in stability through co-digestion.

Enhancement of food waste thermophilic anaerobic digestion through synergistic effect with chicken manure

The role of organic load and ammonia inhibition in anaerobic digestion of tannery fleshing

Mathematical modelling of anaerobic digestion is widely acknowledged as a powerful tool to improve the understanding of the process and to support full-scale plant design, operation and optimization. In this work, a modified version of the IWA-ADM1 model is proposed to simulate the anaerobic digestion of tannery primary sludge and fleshing, with special emphasis on the disintegration formulation. Multiple batch tests were performed at different inoculum/substrate VS-mass ratio, in order to evaluate the biodegradability of the two substrates and to provide experimental data for modelling purposes. Beside the necessary adjustments of substrates’ COD fractionation, the structure modifications of the model focused on the disintegration and hydrolysis. The Contois Monod-based model was adopted to describe disintegration kinetics and the results were compared to the traditionally adopted first-order kinetic. The fate of particulate matter generated from biomass lysis was also questioned and a new model variable was introduced to account for cellular lysis products. Finally, a further modification differentiated substrate particulate matter into a readily and a slowly hydrolysable fraction. Batch tests confirmed that tannery primary sludge and fleshing are suitable substrates for anaerobic digestion, exhibiting specific methane productions of: 0.26±0.06 and 0.47±0.05 Nm3Kg-1VS, respectively. Modelling results showed that the proposed modifications were crucial for successful simulation of experimental data referring to fleshing, whereas did not have a significant effect on the results related to primary sludge degradation. This work is the first application of an IWA-ADM1-based model to anaerobic digestion of tannery waste.

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Modeling the disintegration process in anaerobic digestion of tannery sludge and fleshing

Successful sulphide-driven partial denitrification: Efficiency, stability and resilience in SRT-controlled conditions.

When treating wastewaters prone to inert precipitation with granular sludge systems, mineral formation needs to be properly controlled to ensure system’s long-term stability. In this work, an extensive study on mineral precipitation on the surface of anammox granular sludge is presented. A 7-L reactor was inoculated with one-year stored biomass and volumetric load up to 0.48 gN-NO2-/l/d were achieved, with nitrite removal above 95% and total nitrogen removal rate of almost 1 gN/l/d. Severe mineral precipitation was observed on the granules’ surface after three months of hard-water feeding and resulted in a dramatic deterioration of reactor performance and biomass activity. Substrate diffusion limitation in the inner layers, insufficient mixing due to higher granule density and biofilm erosion due to shear stress increase were deemed the main mechanisms that lead to progressive process disruption. Gravimetric selection was applied to discard granules affected by precipitation and allowed for process restoration. Microbial community analyses revealed that mineral composition possibly affected competition between “Ca. Brocadia” and “Ca. Kuenenia”. The knowledge gathered in the present study details the dramatic consequences on process performance lead by severe mineral precipitation and it is presented as a warning for full-scale applications treating wastewaters prone to precipitation. 

Cecilia Polizzi

Papers

The role of organic load and ammonia inhibition in anaerobic digestion of tannery fleshing

Modeling the disintegration process in anaerobic digestion of tannery sludge and fleshing

Successful sulphide-driven partial denitrification: Efficiency, stability and resilience in SRT-controlled conditions.

Long-term effects of mineral precipitation on process performance, granules' morphology and microbial community in anammox granular sludge

A modified version of the adm1 hydrolysis formulation for simulating anaerobic digestion of tannery sludge and waste