Influences of Temperature and Substrate Particle Content on Granular Sludge Bed Anaerobic Digestion

A perspective on the combination of alkali pre-treatment with bioaugmentation to improve biogas production from lignocellulose biomass

Anaerobic digestion (AD) is a bioprocess technology that integrates into circular economy systems, which produce renewable energy and biofertilizer whilst reducing greenhouse gas emissions. However, improvements in biogas production efficiency are needed in dealing with lignocellulosic biomass. The state-of-the-art of AD technology is discussed, with emphasis on feedstock digestibility and operational difficulty. Solutions to these challenges including for pre-treatment and bioaugmentation are reviewed. This article proposes an innovative integrated system combining alkali pre-treatment, temperature-phased AD and bioaugmentation techniques. The integrated system as modelled has a targeted potential to achieve a biodegradability index of 90% while increasing methane production by 47% compared to conventional AD. The methane productivity may also be improved by a target reduction in retention time from 30 to 20 days. This, if realized has the potential to lower energy production cost and the levelized cost of abatement to facilitate an increased resource of sustainable commercially viable biomethane.

Removal of denatured protein particles enhanced UASB treatment of oxytetracycline production wastewater

Enhanced hydrolysis, which can selectively destroy antibiotic potency, has been previously demonstrated to be an effective pretreatment technology for the biological treatment of antibiotic production wastewater. However, full-scale application of enhanced hydrolysis to the treatment of real oxytetracycline production wastewater showed that the up-flow anaerobic sludge blanket (UASB) reactors treating the pretreated wastewater could only be stable under a low organic loading rate (OLR) of 1.8 ± 0.4 g·COD/L/d. Deterioration of UASB was also confirmed in treating the same wastewater using a bench-scale reactor (R1) at an OLR of 4.4 ± 0.3 g·COD/L/d. Assuming that the particles formed due to the denaturation of soluble proteins under the hydrolysis temperature (110 °C), resulting in the significant increase of suspended solids (SS) in oxytetracycline production wastewater from less than 200 mg/L to 1200 ± 500 mg/L, were responsible for the deterioration of UASB, the pretreated wastewater was filtered using polypropylene cotton fiber and ultrafiltration membrane, and then fed into two parallel bench-scale UASB reactors (R2 and R3). Both reactors maintained a stable COD removal (53.2% ~ 61.1%) even at an OLR as high as 8.0 g·COD/L/d. When the feed of R3 was switched to unfiltered wastewater, however, deterioration of the reactor occurred again. Microscopic observation showed that the granules in R3 were fully covered by protein particles after the switch of the feed. It was possible that the tight layer of the denatured protein particles blocked the inner pores of the granules, resulting in the obstruction of substrate transfer and biogas emission, while removing the protein particles could abate such blockage problem. This study provides a scientific basis for the efficient treatment of antibiotic production wastewater.

A Review of the State of the Art of Biomethane Production: Recent Advancements and Integration of Renewable Energies

Anaerobic Digestion (AD) is a well-established process that is becoming increasingly popular, especially as a technology for organic waste treatment; the process produces biogas, which can be upgraded to biomethane, which can be used in the transport sector or injected into the natural gas grid. Considering the sensitivity of Anaerobic Digestion to several process parameters, mathematical modeling and numerical simulations can be useful to improve both design and control of the process. Therefore, several different modeling approaches were presented in the literature, aiming at providing suitable tools for the design and simulation of these systems. The purpose of this study is to analyze the recent advancements in the biomethane production from different points of view. Special attention is paid to the integration of this technology with additional renewable energy sources, such as solar, geothermal and wind, aimed at achieving a fully renewable biomethane production. In this case, auxiliary heat may be provided by solar thermal or geothermal energy, while wind or photovoltaic plants can provide auxiliary electricity. Recent advancements in plants design, biomethane production and mathematical modeling are shown in the paper, and the main challenges that these fields must face with are discussed. Considering the increasing interest of industries, public policy makers and researchers in this field, the efficiency and profitability such hybrid renewable solutions for biomethane production are expected to significantly improve in the next future, provided that suitable subsidies and funding policies are implemented to support their development.

Biogas production from anaerobic co-digestion using kitchen waste and poultry manure as substrate-part 1: substrate ratio and effect of temperature

The rapidly declining fossil fuels are no longer able to meet the ever-increasing energy demand. Moreover, they are considered responsible for greenhouse gas (GHG) emission, contributing to the global warming. On the other hand, organic wastes, such as kitchen waste (KW) and poultry manure (PM), represent considerable pollution threat to the environment, if not properly managed. Therefore, anaerobic co-digestion of KW and PM could be a sustainable way of producing clean and renewable energy in the form of biogas while minimizing environmental impact. In this study, the anaerobic co-digestion of KW with PM was studied to assess the rate of cumulative biogas (CBG) production and methane percentage in four digester setups (D1, D2, D3, and D4) operated in batch mode. Each digester setup consisted of five parallelly connected laboratory-scale digesters having a capacity of 1 L each. The digester setups were fed with KW and PM at ratios of 1:0 (D1), 1:1 (D2), 2:1 (D3), and 3:1 (D4) at a constant loading rate of 300 mg/L with 50 gm cow manure (CM) as inoculum and were studied at both room temperature (28 °C) and mesophilic temperature (37 °C) over 24 days. The co-digestion of KW with PM demonstrated a synergistic effect which was evidenced by a 16% and 74% increase in CBG production and methane content, respectively, in D2 over D1. The D3 with 66.7% KW and 33.3% PM produced the highest CBG and methane percentage (396 ± 8 mL and 36%) at room temperature. At mesophilic condition, all the digesters showed better performance, and the highest CBG (920 ± 11 mL) and methane content (48%) were observed in D3. The study suggests that co-digestion of KW and PM at mesophilic condition might be a promising way to increase the production of biogas with better methane composition by ensuring nutrient balance, buffering capacity, and stability of the digester.

Up-Flow Anaerobic Sludge Blanket (UASB) Technology for Energy Recovery: A Review on State-of-the-Art and Recent Technological Advances

Up-flow anaerobic sludge blanket (UASB) reactor belongs to high-rate systems, able to perform anaerobic reaction at reduced hydraulic retention time, if compared to traditional digesters. In this review, the most recent advances in UASB reactor applications are critically summarized and discussed, with outline on the most critical aspects for further possible future developments. Beside traditional anaerobic treatment of soluble and biodegradable substrates, research is actually focusing on the treatment of refractory and slowly degradable matrices, thanks to an improved understanding of microbial community composition and reactor hydrodynamics, together with utilization of powerful modeling tools. Innovative approaches include the use of UASB reactor for nitrogen removal, as well as for hydrogen and volatile fatty acid production. Co-digestion of complementary substrates available in the same territory is being extensively studied to increase biogas yield and provide smooth continuous operations in a circular economy perspective. Particular importance is being given to decentralized treatment, able to provide electricity and heat to local users with possible integration with other renewable energies. Proper pre-treatment application increases biogas yield, while a successive post-treatment is needed to meet required effluent standards, also from a toxicological perspective. An increased full-scale application of UASB technology is desirable to achieve circular economy and sustainability scopes, with efficient biogas exploitation, fulfilling renewable energy targets and green-house gases emission reduction, in particular in tropical countries, where limited reactor heating is required.

Food waste leachate treatment using an Upflow Anaerobic Sludge Bed (UASB): Effect of conductive material dosage under low and high organic loads

In this study, the performance of UASB for treating food waste leachate was investigated, with the objective of studying the effect of conductive material on anaerobic digestion (AD) enhancement at two organic loads. Conductive and control materials (i.e. graphite and glass) were first compared for their surface porosity then dosed in UASB for side-by-side comparison of the corresponding AD performance. In the first phase (organic load of 2660 mg-COD/L), compared to glass-added UASB, 29.5% reduction of effluent COD was observed in graphite-added UASB, however, only a little biogas enhancement (2.3%) was achieved. In the second phase (organic load of 4140 mg-COD/L), the results show that it could promote better AD enhancement in graphite-added UASB, where 36% effluent COD and 38% biogas production enhancement were simultaneously observed. The overall results support that utilization of conductive material is a viable approach for enhancing biogas production in UASB, especially for high organic loads.