Bioelimination of low methane concentrations emitted from wastewater treatment plants: a review

Prolonged operation of a methane biofilter from acclimation to the failure stage

Global warming needs immediate attention to reduce major greenhouse gas emissions such as methane (CH4). Bio-oxidation of dilute CH4 emissions in packed-bed bioreactors such as biofilters has been carried out over recent years at laboratory and large scales. However, a big challenge is to keep CH4 biofilters running for a long period. In this study, a packed-bed lab-scale bioreactor with a specialized inorganic-based filter bed was successfully operated over four years for CH4 elimination. The inoculation of the bioreactor was the active leachate of another CH4 biofilter which resulted in a fast acclimation and removal efficiency (RE) reached 80% after seven weeks of operation for CH4 inlet concentrations ranging from 700 to 800 ppmv and an empty bed residence time (EBRT) of 6 min. During four years of operation, the bioreactor often recorded REs higher than 65% for inlet concentrations in the range of 1900-2200 ppmv and an EBRT of 6 min. The rate and interval of the nutrient supply played an important role in maintaining the bioreactor's high performance over the long operation. Forced shutdowns were unavoidable during the 4-year operation and the bioreactor fully tolerated them with a partial recovery within one week and a progressive recovery over time. In the end, the bioreactor's filter bed started to deteriorate due to a long shutdown of twelve weeks and the extended operation of four years when the RE dropped to below 8% with no sign of returning to its earlier performance.

Microaerobic methane-driven denitrification in a biotrickle bed - Investigating the active microbial biofilm community composition using RNA-stable isotope probing

A microaerobic (2% O2 v/v) biotrickle bed reactor supplied continuously with 2% methane to drive nitrate removal (MAME-D) was investigated using 16S rDNA and rRNA amplicon sequencing in combination with RNA-stable isotope probing (RNA-SIP) to identify the active microorganisms. Methane removal rates varied from 500 to 1000 mmol m-3h-1 and nitrate removal rates from 25 to 58 mmol m-3h-1 over 55 days of operation. Biofilm samples from the column were incubated in serum bottles supplemented with 13CH4. 16S rDNA analysis indicated a simple community structure in which four taxa accounted for 45% of the total relative abundance (RA). Dominant genera included the methanotroph Methylosinus and known denitrifiers Nubsella and Pseudoxanthomonas; along with a probable denitrifier assigned to the order Obscuribacterales. The 16S rRNA results revealed the methanotrophs Methylocystis (15% RA) and Methylosinus (10% RA) and the denitrifiers Arenimonas (10% RA) and Pseudoxanthomonas (7% RA) were the most active genera. Obscuribacterales was the most active taxa in the community at 22% RA. Activity was confirmed by the Δ buoyant density changes with time for the taxa, indicating most of the community activity was associated with methane oxidation and subsequent consumption of methanotrophic metabolic intermediates by the denitrifiers. This is the first report of RNA stable isotope probing within a microaerobic methane driven denitrification system and the active community was markedly different from the full community identified via 16S-rDNA analysis.

Sustainability for wastewater treatment: bioelectricity generation and emission reduction

This review covers the technological measures of a self-sustainable anaerobic up-flow sludge blanket (UASB) system compared with an aerobic activated sludge process (ASP) for wastewater treatment plants (WWTPs). The ASP requires a huge amount of electricity and chemicals and also results in the emission of carbon. The UASB system, instead, is based on greenhouse gas (GHG) emission reduction and is associated with biogas production for cleaner electricity. WWTPs including the ASP system are not sustainable due to the massive financial power required for clean wastewater. When the ASP system was used, the amount of production was estimated to be 10658.98 tonnes CO₂eq-d^- of carbon dioxide. Whereas it was 239.19 tonnes CO₂eq-d^-1 with the UASB. The UASB system is advantageous over the ASP system as it has a high production of biogas, needs low maintenance, yields a low amount of sludge, and is also a source of electricity that can be used as a power source for the WWTPs. Also, the UASB system produces less biomass, and this helps in reducing costs and maintaining work. Moreover, the aeration tank of the ASP needs 60% of energy distribution; on the other hand, the UASB consumes less energy, approximately 3-11%.

A review on biofiltration techniques: Recent advancements in the removal of volatile organic compounds and heavy metals in the treatment of polluted water

Good quality of water determines the healthy life of living beings on this earth. The cleanliness of water was interrupted by the pollutants emerging out of several human activities. Industrialization, urbanization, heavy population, and improper disposal of wastes are found to be the major reasons for the contamination of water. Globally, the inclusion of volatile organic compounds (VOCs) and heavy metals released by manufacturing industries, pharmaceuticals, and petrochemical processes have created environmental issues. The toxic nature of these pollutants has led researchers, scientists, and industries to exhibit concern towards the complete eradication of them. In this scenario, the development of wastewater treatment methodologies at low cost and in an eco-friendly way had gained importance at the international level. Recently, bio-based technologies were considered for environmental remedies. Biofiltration based works have shown a significant result for the removal of volatile organic compounds and heavy metals in the treatment of wastewater. This was done with several biological sources such as bacteria, fungi, algae, plants, yeasts, etc. The biofiltration technique is cost-effective, simple, biocompatible, sustainable, and eco-friendly compared to conventional techniques. This review article provides deep insight into biofiltration technologies engaged in the removal of volatile organic compounds and heavy metals in the wastewater treatment process.