Carbon balance of anaerobic granulation process: carbon credit

Anaerobic-aerobic treatment of high-strength and recalcitrant textile dyeing effluents

Eco-friendly treatment of complex textile and dyeing wastewaters poses a pressing environmental concern. An approach adopting different treatment paths and integrated anaerobic-aerobic processes for high-strength and recalcitrant textile dyeing wastewater was examined. The study demonstrated that over 97% of suspended solids (SS) and more than 70% of chemical oxygen demand (COD) were removed by polyaluminum chloride pre-coagulation of suede fabric dyeing stream. Up to 58% of COD and 83% of SS were removed through hydrolysis pretreatment of other low-strength streams. Notable COD removal of up to 99% from a feed of 20,862 mg COD/L was achieved by integrated anaerobic-aerobic treatment of high strength stream. Besides achieving high COD removal of 97%, the anaerobic granular sludge process demonstrated multi-faceted attributes, including high feed loading, smaller footprint, little sludge production, and good stability. The integrated anaerobic-aerobic treatment offers a robust and viable option for highly contaminated and recalcitrant textile dyeing wastewater.

A high-value biohythane production: Feedstocks, reactor configurations, pathways, challenges, technoeconomics and applications

In recent years, the demand for high-quality biofuels from renewable sources has become an aspirational goal to offer a clean environment by alternating the depleting fossil fuels to meet future energy needs. In this aspect, biohythane production from wastes has received extensive research interest since it contains superior fuel characteristics than the promising conventional biofuel i.e. biogas. The main aim is to promote research and potentials of biohythane production by a systematic review of scientific literature on the biohythane production pathways, substrate/microbial consortium suitability, reactor design, and influential process/operational factors. Reactor configuration also decides the product yield in addition to other key factors like waste composition, temperature, pH, retention time and loading rates. Hence, a detailed emphasis on different reactor configurations with respect to the type of feedstock has also been given. The technical challenges are highlighted towards process optimization and system scale up. Meanwhile, solutions to improve product yield, technoeconomics, applications and key policy and governance factors to build a hydrogen based society have also been discussed.

Integrated Anaerobic/Oxic/Oxic treatment for high strength palm oil mill effluent

Safe disposal of effluent from palm oil production poses an environmental concern. The highly polluting effluent is customarily treated by unsustainable open ponds with low efficiency, direct emissions, and massive land use. This study looks into an application of integrated anaerobic/oxic/oxic scheme for treatment of high strength palm oil mill effluent. The anaerobic reactors functioned as a prime degrader that removed up to 97.5% of the chemical oxygen demand (COD), while the aerobic reactors played a role of an effluent polisher that further reduced the COD. Their complementing roles resulted in a remarkable removal of 99.7%. Assessment of emission mitigation and biogas energy revealed that yearly energy of 53.2 TJ, emissions reduction of 239,237 tCO₂ and revenue of USD 1.40 millions can be generated out of electricity generation and heating. The integrated scheme provides a viable and sustainable treatment of the high strength palm oil mill effluent.

High-rate blackwater anaerobic digestion under septic tank conditions with the amendment of biosolids-derived biochar synthesized at different temperatures

Septic tanks have been widely used for blackwater treatment in developing countries, while high-rate septic tanks with improved methane recovery are yet to be achieved. This study investigated biosolids-derived biochar (synthesized at 300℃, 425℃, and 550℃) as an additive for developing high-rate septic tanks. The experiments were conducted with anaerobic bioreactors operated with synthetic blackwater under septic tank conditions. All biochar amended reactors demonstrated a steady increase in daily methane production for increasing OLR from 0.08 to 3 g COD/L/d. The control reactor showed significant process disturbances at OLRs ≥ 2 g COD/L/d with an accumulation of volatile fatty acids followed by pH drop. At OLR of 3 g COD/L/d, the daily methane production from biochar amended reactors was ~ 4.3 times higher than the control (300 vs. 70 mL per day). Biochar addition established a robust microbiome consisted of a higher abundance of hydrogenotrophic and acetoclastic methanogens and hydrogen-producing fermentative bacteria.

Biomethane Potential of Sludges from a Brackish Water Fish Hatchery

The development of intensive aquaculture is facing the challenge of the sustainable management of effluents. The reproductive sectors (i.e., hatcheries) mainly use water recirculation systems (RAS), which discharge a portion of wastewater. Anaerobic digestion (AD) could reduce the environmental impact of this waste stream while producing biogas. The study is focused on the biochemical methane potential (BMP) of brackish fish hatchery sludges. Wastewater was concentrated by microfiltration and sedimentation and thickened sludges were treated in a BMP system with different inoculum/substrate (I/S) volatile solids ratios (from 50:1 to no inoculum). The highest I/S ratio showed the highest BMP (564.2 NmL CH4/g VS), while different I/S ratios showed a decreasing trend (319.4 and 127.7 NmL CH4/g VS, for I/S = 30 and I/S = 3). In absence of inoculum BMP resulted of 62.2 NmL CH4/g VS. The kinetic analysis (modified Gompertz model) showed a good correlation with the experimental data, but with a long lag-phase duration (from 14.0 to 5.5 days) in particular with the highest I/S. AD applied to brackish water sludges can be a promising treatment with interesting methane productions. For a continuous, full-scale application further investigation on biomass adaptation to salinity and on retention times is needed. Further experimental tests are ongoing.

Anaerobic granulation: A review of granulation hypotheses, bioreactor designs and emerging green applications

Successful installations and operation of many granulation-base treatment plants all over the world in the recent years are reported. A better knowledge towards reactor operation and system performance has led to a growing interest in the technology. While the technology is well accepted and abundant research work has been carried out, insight unfolding the granulation fundamentals and its engineering applications remains unclear. This paper presents a review of some major hypotheses describing the evolvement of anaerobic granules. A number of physico-chemical hypotheses based on thermodynamics and structural hypotheses incorporating microbial considerations for anaerobic granulation have been developed. Features of anaerobic granulation and bioreactor designs are also reviewed. Advances in granulation research with respect to hydrogen production, degradation of recalcitrant or toxic compounds and emissions mitigation are delineated. Prospects and challenges of anaerobic granulation in wastewater treatment are also outlined.

Biohythane production via single-stage anaerobic fermentation using entrapped hydrogenic and methanogenic bacteria

This study demonstrates the continuous biohythane production in a single-stage anaerobic digester using a biomass mixture of separately entrapped hydrogenic and methanogenic bacteria (H₂- and CH₄-producing bacteria, respectively). The entrapped hydrogenic/methanogenic bacteria biomass ratios of 1/4, 2/3, 3/2 and 4/1 were tested and shown to have a great effect on the single-stage biohythane production performance. At steady-states, the cultivations had biohythane production rates in the range of 381-480 mL/L-d, with H₂ content in biohythane (HCH) varying from 1% to 75% (v/v) and chemical oxygen demand removal efficiencies (TCOD_re) of 57.6-81.9%. Biomass ratio 2/3 (weight ratio 1/1.5) resulted in peak biohythane production with H₂ and CH₄ production rates being 64.6 and 395 mL/L-d, respectively, HCH 15% and TCOD_re 74.4%. The novelty of this work is to show the potential of producing biohythane from an innovative single-stage dark fermentation system using entrapped hydrogenic and methanogenic bacteria.

Determination of greenhouse gas emission reductions from sewage sludge anaerobic digestion in China

Sewage sludge is a considerable source of greenhouse gas (GHG) emission in the field of organic solid waste treatment and disposal. In this case study, total GHG emissions from sludge anaerobic digestion, including direct and indirect emissions as well as replaceable emission reduction due to biogas being reused instead of natural gas, were quantified respectively. The results indicated that no GHG generation needed to be considered during the anaerobic digestion process. Indirect emissions were mainly from electricity and fossil fuel consumption on-site and sludge transportation. Overall, the total GHG emission owing to relative subtraction from anaerobic digestion rather than landfill, and replaceable GHG reduction caused by reuse of its product of biogas, were quantified to be 0.7214 (northern China) or 0.7384 (southern China) MgCO2 MgWS(-1) (wet sludge).