An advanced anaerobic biofilter with effluent recirculation for phenol removal and methane production in treatment of coal gasification wastewater

An advanced anaerobic biofilter (AF) was introduced for the treatment of coal gasification wastewater (CGW), and effluent recirculation was adopted to enhance phenol removal and methane production. The results indicated that AF was reliable in treating diluted CGW, while its efficiency and stability were seriously reduced when directly treating raw CGW. However, its performance could be greatly enhanced by effluent recirculation. Under optimal effluent recirculation of 0.5 to the influent, concentrations of chemical oxygen demand (COD) and total phenol in the effluent could reach as low as 234.0 and 14.2 mg/L, respectively. Also, the rate of methane production reached 169.0 mL CH₄/L/day. Though CGW seemed to restrain the growth of anaerobic microorganisms, especially methanogens, the inhibition was temporary and reversible, and anaerobic bacteria presented strong tolerance. The activities of methanogens cultivated in CGW could quickly recover on feeding with glucose wastewater (GW). However, the adaptability of anaerobic bacteria to the CGW was very poor and the activity of methanogens could not be improved by long-term domestication. By analysis using the Haldane model, it was further confirmed that high effluent recirculation could result in high activity for hydrolytic bacteria and substrate affinity for toxic matters, but only suitable effluent recirculation could result in high methanogenic activity.     

Determination of biogas generation potential as a renewable energy source from supermarket wastes

Fruit, vegetable, flower waste (FVFW), dairy products waste (DPW), meat waste (MW) and sugar waste (SW) obtained from a supermarket chain were anaerobically digested, in order to recover methane as a source of renewable energy. Batch mesophilic anaerobic reactors were run at total solids (TS) ratios of 5%, 8% and 10%. The highest methane yield of 0.44 L CH₄/g VS_added was obtained from anaerobic digestion of wastes (FVFW + DPW + MW + SW) at 10% TS, with 66.4% of methane (CH₄) composition in biogas. Anaerobic digestion of mixed wastes at 5% and 8% TS provided slightly lower methane yields of 0.41 and 0.40 L CH₄/g VS_added, respectively. When the wastes were digested alone without co-substrate addition, the highest methane yield of 0.40 L CH₄/g VS_added was obtained from FVFW at 5% TS. Generally, although the volatile solids (VS) conversion percentages seemed low during the experiments, higher methane yields could be obtained from anaerobic digestion of supermarket wastes. A suitable carbon/nitrogen (C/N) ratio, proper adjustment of the buffering capacity and the addition of essential trace nutrients (such as Ni) could improve VS conversion and biogas production yields significantly.     

Effects of thermobarical pretreatment of cattle waste as feedstock for anaerobic digestion

Lab-scale experiments were conducted to assess the impact of thermobarical treatment of cattle waste on anaerobic digestion. Treatment was at temperatures of 140–220 °C in 20 K steps for a 5-min duration. Methane yields could be increased by up to 58% at a treatment temperature of 180 °C. At 220 °C the abundance of inhibitors and other non-digestible substances led to lower methane yields than those obtained from untreated material. In an extended analysis it could be demonstrated that there is a functional correlation between the methane yields after 30 days and the formation rate and methane yield in the acceleration phase. It could be proved in a regression of these correlation values that the optimum treatment temperature is 164 °C and that the minimum treatment temperature should be above 115 °C.     

Characterizing food waste substrates for co-digestion through biochemical methane potential (BMP) experiments

Co-digestion of food waste with dairy manure is increasingly utilized to increase energy production and make anaerobic digestion more affordable; however, there is a lack of information on appropriate co-digestion substrates. In this study, biochemical methane potential (BMP) tests were conducted to determine the suitability of four food waste substrates (meatball, chicken, cranberry and ice cream processing wastes) for co-digestion with flushed dairy manure at a ratio of 3.2% food waste and 96.8% manure (by volume), which equated to 14.7% (ice-cream) to 80.7% (chicken) of the VS being attributed to the food waste. All treatments led to increases in methane production, ranging from a 67.0% increase (ice cream waste) to a 2940% increase (chicken processing waste) compared to digesting manure alone, demonstrating the large potential methane production of food waste additions compared to relatively low methane production potential of the flushed dairy manure, even if the overall quantity of food waste added was minimal.     

Influence of NOx on the activity of Pd/θ-Al2O3 catalyst for methane oxidation: Alleviation of transient deactivation

Alumina supported Pd catalyst（Pd/Al₂O₃） is active for complete oxidation of methane, while often suffers transient deactivation during the cold down process. Herein, heating and cooling cycle tests between 200 and 900 °C and isothermal experiments at 650 °C were conducted to investigate the influence of NO_x on transient deactivation of Pd/θ-Al₂O₃ catalyst during the methane oxidation. It was found that the co-fed of NO alleviated transient d...     

Methane fluxes from artificial wetlands: A global appraisal

Methane emissions make an important contribution to the enhanced greenhouse effect, emissions from rice growing being one of its major anthropogenic sources. The estimation of global fluxes of methane from rice and from coarse fiber production depends on extrapolating observed data across countries and agroclimatic zones: the estimates are therefore imprecise. We present a revised estimate of global emissions of 96 Tg CH₄/yr, given 1991 rice areas, and 1991 production data for those tropical coarse fibers that also produce methane under anaerobic conditions. This is higher than many previous studies, which systematically underestimated the fluxes from tropical countries. As the world's population increases, the demand for rice will rise. This demand can only be satisfied through greater rice production, either by bringing new areas into rice growing or by using the present area more intensively. Strategies based on improved water management and fertilizer use will allow increased rice production and yields and reduce the methane flux per unit or rice production.     

Nitrous oxide and methane in a changing Arctic Ocean

Human activities are changing the Arctic environment at an unprecedented rate resulting in rapid warming, freshening, sea ice retreat and ocean acidification of the Arctic Ocean. Trace gases such as nitrous oxide (N₂O) and methane (CH₄) play important roles in both the atmospheric reactivity and radiative budget of the Arctic and thus have a high potential to influence the region’s climate. However, little is known about how these rapid physical and chemical changes will impact the emissions of major climate-relevant trace gases from the Arctic Ocean. The combined consequences of these stressors present a complex combination of environmental changes which might impact on trace gas production and their subsequent release to the Arctic atmosphere. Here we present our current understanding of nitrous oxide and methane cycling in the Arctic Ocean and its relevance for regional and global atmosphere and climate and offer our thoughts on how this might change over coming decades.Supplementary InformationThe online version contains supplementary material available at 10.1007/s13280-021-01633-8.     

煤层气开发环境影响浅析

在国际能源局势趋紧的情况下,作为一种优质高效清洁能源,煤层气具有广阔的开发前景。我国煤层气开发仍处于起步阶段,因此,煤层气开发对环境的影响应该引起关注。文章分析了煤层气开发对水环境、生态环境、大气环境及声环境的影响,对探索并形成系统有效的环保措施有一定参考价值。     

Greenhouse gas production and efficiency of planted and artificially aerated constructed wetlands

Greenhouse gas (GHG) emissions by constructed wetlands (CWs) could mitigate the environmental benefits of nutrient removal in these man-made ecosystems. We studied the effect of 3 different macrophyte species and artificial aeration on the rates of nitrous oxide (N₂O), carbon dioxide (CO₂) and methane (CH₄) production in CW mesocosms over three seasons. CW emitted 2-10 times more GHG than natural wetlands. Overall, CH₄ was the most important GHG emitted in unplanted treatments. Oxygen availability through artificial aeration reduced CH₄ fluxes. Plant presence also decreased CH₄ fluxes but favoured CO₂ production. Nitrous oxide had a minor contribution to global warming potential (GWP < 15%). The introduction of oxygen through artificial aeration combined with plant presence, particularly Typha angustifolia, had the overall best performance among the treatments tested in this study, including lowest GWP, greatest nutrient removal, and best hydraulic properties.     

High methane emissions from a littoral zone on the Qinghai-Tibetan Plateau

The littoral zones of lakes have been regarded as hotspots of methane (CH₄) fluxes through several studies. In the present study, we measured CH₄ fluxes in six kinds of littoral zones of Huahu Lake on the Qinghai-Tibetan Plateau in the peak growing season of 2006 and 2007. We found that CH₄ efflux (ranging from −0.1 to 90 mg CH₄ m⁻² h⁻¹) from the littoral zones of this lake was relatively high among those of boreal and temperate lakes. Our results also showed that emergent plant zones (Hippuris vulgaris and Glyceria maxima stands) recorded the highest CH₄ flux rate. The CH₄ flux in the floating mat zone of Carex muliensis was significantly lower than those of the emergent plant zones. CH₄ fluxes in the floating-leaved zone of Polygonum amphibium and bare lakeshore showed no significant difference and ranked last but one, only higher than that of the littoral meadow (Kobresia tibetica). Plant biomass and standing water depths were important factors to explain such spatial variations in CH₄ fluxes. No significant temporal variations in CH₄ fluxes were found due to the insignificant variations of physical factors in the peak growing season. These results may help in our understanding of the importance of the littoral zone of lakes, especially the emergent plant zone, as a hotspot of CH₄ emission.