Optimisation of bioscrubber systems to simultaneously remove methane and purify wastewater from intensive pig farms

The use of bioscrubber is attracting increasing attention for exhaust gas treatment in intensive pig farming. However, the challenge is to improve the methane (CH4) removal efficiency as well as the possibility of pig house wastewater treatment. Three laboratory-scale bioscrubbers, each equipped with different recirculation water types, livestock wastewater (10-times-diluted pig house wastewater supernatant), a methanotroph growth medium (10-times-diluted), and tap water, were established to evaluate the performance of CH4 removal and wastewater treatment. The results showed that enhanced CH4 removal efficiency (25%) can be rapidly achieved with improved methanotrophic activity due to extra nutrient support from the wastewater. The majority of the CH4 was removed in the middle to end part of the bioscrubbers, which indicated that CH4 removal could be potentially optimised by extending the length of the reactor. Moreover, 52–86% of the ammonium (NH4+-N), total organic carbon (TOC), and phosphate (PO43−-P) removal were simultaneously achieved with CH4 removal in the present study. Based on these results, this study introduces a low-cost and simple-to-operate method to improve CH4 removal and simultaneously treat pig farm wastewater in bioscrubbers

Stoichiometric analysis of nutrient availability (N, P, K) within soils of polygonal tundra

Plant growth in arctic tundra is known to be commonly limited by nitrogen. However, biogeochemical interactions between soil, vegetation and microbial biomass in arctic ecosystems are still insufficiently understood. In this study, we investigated different compartments of the soil-vegetation system of polygonal lowland tundra: bulk soil, inorganic nutrients, microbial biomass and vegetation biomass were analyzed for their contents of carbon, nitrogen, phosphorus and potassium. Samples were taken in August 2011 in the Indigirka lowlands (NE Siberia, Russia) in a detailed grid (4 m × 5 m) in one single ice-wedge polygon. We used a stoichiometric approach, based on the N/P ratios in the vegetation biomass and the investigated soil fractions, to analyze limitation relations in the soil-vegetation system. Plant growth in the investigated polygonal tundra appears to be co-limited by nitrogen and phosphorus or in some cases only limited by nitrogen whereas potassium is not limiting plant growth. However, as the N/P ratios of the microbial biomass in the uppermost soil horizons were more than twice as high as previously reported for arctic ecosystems, nitrogen mineralization and fixation may be limited at present by phosphorus. We found that only 5 % of the total nitrogen is already cycling in the biologically active fractions. On the other hand, up to 40 % of the total phosphorus was found in the biologically active fractions. Thus, there is less potential for increased phosphorus mineralization than for increased nitrogen mineralization in response to climate warming, and strict phosphorus limitation might be possible in the long-term

High methane emissions dominated annual greenhouse gas balances 30 years after bog rewetting

Natural peatlands are important carbon sinks and sources of methane (CH₄). In contrast, drained peatlands turn from a carbon sink to a carbon source and potentially emit nitrous oxide (N₂O). Rewetting of peatlands thus potentially implies climate change mitigation. However, data about the time span that is needed for the re-establishment of the carbon sink function by restoration are scarce. We therefore investigated the annual greenhouse gas (GHG) balances of three differently vegetated sites of a bog ecosystem 30 years after rewetting. All three vegetation communities turned out to be sources of carbon dioxide (CO₂) ranging between 0.6 ± 1.43 t CO₂ ha⁻² yr⁻¹ (<i>Sphagnum-</i>dominated vegetation) and 3.09 ± 3.86 t CO₂ ha⁻² yr⁻¹ (vegetation dominated by heath). While accounting for the different global warming potential (GWP) of CO₂, CH₄ and N₂O, the annual GHG balance was calculated. Emissions ranged between 25 and 53 t CO₂-eq ha⁻¹ yr⁻¹ and were dominated by large emissions of CH₄ (22–51 t CO₂-eq ha⁻¹ yr⁻¹), with highest rates found at purple moor grass (<i>Molinia caerulea</i>) stands. These are to our knowledge the highest CH₄ emissions so far reported for bog ecosystems in temperate Europe. As the restored area was subject to large fluctuations in the water table, we assume that the high CH₄ emission rates were caused by a combination of both the temporal inundation of the easily decomposable plant litter of purple moor grass and the plant-mediated transport through its tissues. In addition, as a result of the land use history, mixed soil material due to peat extraction and refilling can serve as an explanation. With regards to the long time span passed since rewetting, we note that the initial increase in CH₄ emissions due to rewetting as described in the literature is not inevitably limited to a short-term period