Start-up strategies to develop aerobic granular sludge and photogranules in sequential batch reactors

In this study, start-up strategies to develop conventional aerobic granular sludge (AGS) and algal aerobic granular sludge (AAGS) (photogranules), were investigated. The granulation experiment was conducted in four sequencing batch reactors (SBR), of which two were conventional SBRs (RC1, RC2) used as control, and two were photo-SBRs (R1, R2). R1 and RC1 were operated with a 40-min feeding during the reactors´ anaerobic cycle period, whereas R2 and RC2 with a 60-min feeding. All the reactors were operated in two phases with a C:N = 4:1 in Phase I and 8:1 in Phase II. In Phase I, AGS in RC1 and RC2 was formed 15 days before the AAGS development in R1 and R2. However, the AAGS generally presented better stability and higher diameter. On the other hand, AGS presented greater abundance of extracellular polymeric substances producing organisms, such as Xanthomonadacea and Rhodocyclaceae. Chemical oxygen demand (COD) and NH₄⁺-N removal efficiencies were similar in all the four reactors of approximately 70% and 60%, respectively. In this phase, despite the good biomass structure, the reactors were not able to completely oxidize the high influent concentration of NH₄⁺-N (100 mg.L^-1) and COD (400 mg.L^-1). This can be associated to the short time of the aerobic phase and low biomass content. In Phase II in all the reactors, a good increase in COD and NH₄⁺-N removal efficiencies to values above 95% and 93%, respectively, was achieved under a higher C:N ratio of 8 with lower influent concentration of NH₄⁺-N (50 mg.L^-1). The 60-min anaerobic feeding period in R2 and RC2 resulted in greater removal efficiency of nitrogen, confirming that small variation on cycle periods can affect the biomass composition; the biomass presented more compact granules and larger diameters under 60 min-feeding when compared with those obtained with 40 min-feeding in Phase I.

Dispersal of cellulose fibers and metals from contaminated sediments of industrial origin in an estuary

The boreal forest's pulp and paper industry plays a major role in economic prosperity but, historically, caused an environmental burden. Remnants of discharges of contaminated suspended solids (fiberbanks) are continuously being discovered on the beds of shallow seas, rivers and lakes in the northern hemisphere. We investigated the dispersion of Cd, Cr, Cu, Hg, Ni, Pb and Zn from deeper to surficial layers in fiberbanks in a Swedish estuary and the larger-scale transport of the same metals to distal areas of sediment accumulation. We also tested the C:N ratio as a common denominator for these anthropogenic, cellulose-rich deposits. Sampling and analyses of three fiberbanks located in the inner part of the estuary and from sediment accumulation sites outside and along the estuary reveals that metal concentrations are regressing to background levels towards the surface at the accumulation sites. The fiberbanks show a higher degree of contamination and C:N ratios demonstrate inclusion of cellulose fibers. C:N ratios also indicate that there is currently no significant transport of fiberbank material into the distal areas. A ∼10 cm natural cap of recently settled fine-grained sediment covering one of the fiberbanks seems to prevent metals dispersing into overlying water whereas the other two fiberbanks show signs of metal enrichment and potential mercury methylation in surficial layers. Although the estuarine system seems to recover from the impact of industrial waste, there is no evidence that the fiberbanks will be remediated naturally but instead will continue to threaten the aquatic environment.

C:N ratio shaped both taxonomic and functional structure of microbial communities in livestock and poultry breeding wastewater treatment reactor

C:N ratios play critical roles in determining the stability and performance of the wastewater treatment reactor. Here, we investigated bacterial and archaeal community composition, diversity, association networks, and functional profiles in livestock and poultry breeding wastewater (LPBW) with C:N gradients from 7.8 to 18.9 using 16S rRNA gene amplicon sequencing. Highest total nitrogen (TN) and total phosphorous (TP) removal rates were detected in the wastewater with high C:N ratios, while bacterial and archaeal communities in the wastewater varied across the four C:N ratios. Proteobacteria, Acidobacteria, and Bacteroides were generally the dominant phyla in the wastewater across treatments, with Candidatus Saccharibacteria being more enriched in the wastewater with high C:N ratios. Association network analysis showed that specific bacterial and archaeal taxa likely have similar metabolic activities allowing them to respond similarly to different C:N ratios. Bacteroidetes, Actinobacteria, Verrucomicrobia, Candidatus Saccharibacteria, and Proteobacteria were the keystone species found in the networks. Most dominant bacterial functions in the wastewater were chemoheterotrophy and aerobic chemoheterotrophy. Nitrite respiration, nitrous oxide denitrification, nitrate denitrification and nitrite denitrification were up-regulated with increased C:N ratios. Our findings provide new insights into our understanding of the compositions, potential associations, and predicted functional profiles of the microbial community in LPBW treated with different C:N ratios.

Permafrost and land cover as controlling factors for light fraction organic matter on the southern Qinghai-Tibetan plateau

Permafrost degradation can stimulate the decomposition of organic soil matter and cause a large amount of greenhouse gas emissions into the atmosphere. The light fraction organic matter (LFOM) is a labile substrate for microbial decomposition and probably plays an important role in future permafrost carbon cycles. However, little is known about the distribution of LFOM and its relationship with permafrost and environmental factors. Here, we investigated the light fraction carbon (LFC) and nitrogen (LFN) contents and stocks under meadows and wet meadows with different permafrost conditions on the southern Qinghai-Tibetan Plateau. Our results showed that LFC and LFN were mainly distributed in the upper 30cm of soils, and the sites with permafrost had significantly higher contents of LFC and LFN than those from the sites without existing permafrost. The LFC and LFN decreased sharply with depth, suggesting that the soil organic matter (SOM) in this area was highly decomposed in deep soils. Soil moisture and bulk density explained approximately 50% of the variances in LFC and LFN for all the sampling sites, while soil moisture explained approximately 30% of the variance in permafrost sites. Both the C:N ratios and LFC:LFN ratios in the sites with permafrost were higher than those in the sites without permafrost. The results suggested that the permafrost and land cover types are the main factors controlling LFOM content and stock, and that permafrost degradation would lead to a decrease of LFOM and soil C:N ratios, thus accelerating the decomposition of SOM.

Understanding litter decomposition in semiarid ecosystems: linking leaf traits, UV exposure and rainfall variability

Differences in litter quality, microbial activity or abiotic conditions cannot fully account for the variability in decomposition rates observed in semiarid ecosystems. Here we tested the role of variation in litter quality, water supply, and UV radiation as drivers of litter decomposition in arid lands. And show that carry-over effects of litter photodegradation during dry periods can regulate decomposition during subsequent wet periods. We present data from a two-phase experiment, where we first exposed litter from a drought-deciduous and an evergreen shrub to natural UV levels during five, rainless summer months and, subsequently, in the laboratory, we assessed the carry-over effects of photodegradation on biomass loss under different irrigation treatments representing the observed range of local rainfall variation among years (15-240 mm). Photodegradation of litter in the field produced average carbon losses of 12%, but deciduous Proustia pungens lost >25%, while evergreen Porlieria chilensis less than 5%. Natural exposure to UV significantly reduced carbon-to-nitrogen and lignin:N ratios in Proustia litter but not in Porlieria. During the subsequent wet phase, remaining litter biomass was lower in Proustia than in Porlieria. Indeed UV exposure increased litter decomposition of Proustia under low and medium rainfall treatments, whereas no carry-over effects were detected under high rainfall treatment. Consequently, for deciduous Proustia carry-over effects of UV exposure were negligible under high irrigation. Litter decomposition of the evergreen Porlieria depended solely on levels of rainfall that promote microbial decomposers. Our two-phase experiment revealed that both the carry-over effects of photodegradation and litter quality, modulated by inter-annual variability in rainfall, can explain the marked differences in decomposition rates and the frequent decoupling between rainfall and litter decomposition observed in semiarid ecosystems.