Potassium supplement enhanced cadmium removal in a Microcystis aeruginosa photobioreactor: Evidence from actual and simulated wastewater.

In this study, a Microcystis aeruginosa-based photobioreactor (M. aeruginosa-based PBR) was developed for the removal of cadmium (Cd2+) from diluted actual mine wastewater (DW) and Cd2+-contained simulated wastewater (SW), with a uniform Cd2+ concentration of 0.5 mg/L. For the DW and SW, both K+ -abundant (DWA & SWA) and K+-insufficient (DWB & SWB) treatments were conducted. It was found that continuous supplementation of K+ benefited Cd2+ removal. The Cd2+ removal efficiency in SWA reached 70% during the 41 days of operation, which was 20% higher than that in the SWB. The K+ addition triggered great higher Cd2+ removal efficiency (90%) in the DWA in comparison to the SWA. The Cd2+ assimilation by M. aeruginosa and Cd2+ retention on M. aeruginosa surface were the primary processes involved in the PBR system. The K+ starvation triggered a 45% and 43% loss of M. aeruginosa biomass in the DWA and the DWB, respectively. Hence, the Cd2+ removal efficiency in DWB increased significantly, and this was attributed to the increased abundance of non-living cells and enhanced bioretention of Cd2+. The results revealed that continuous K+ supplementation enhanced the Cd2+ removal efficiency in the M. aeruginosa-based PBR jointly by prompting algal cell growth, Cd2+ assimilation and biosorption, as well as Cd2+ retention on the algal cells.

Potassium regulates cadmium toxicity in Microcystis aeruginosa.

Microcystis aeruginosa (M. aeruginosa) was found to be capable of cadmium (Cd2+) assimilation. Potassium (K+), an essential factor in transmembrane transport, can possibly manipulate the interaction between Cd2+ and M. aeruginosa. In this study, the effect of available K+ levels on Cd2+ toxicity in M. aeruginosa is examined. The results showed that the K+ level was positively linked with toxicity of Cd2+ to M. aeruginosa. And with respect to the M. aeruginosa incubated in K+ = 460 µM treatment, the release of extracellular polymeric substance was augmented, which benefited the retention of Cd2+ on the M. aeruginosa surface. In addition, the assimilation of Cd2+ showed a 3.42-fold increase in comparison to that without K+ supplement. Moreover, the enhanced K+ level caused the up-regulation of the Cd2+ transporting protein and down-regulation of the Cd2+ efflux protein, associated with the positive energy metabolism response. These results documented that the K+ availability could influence the toxicity of Cd2+ to M. aeruginosa jointly through the manipulation of Cd2+ assimilation, excretion, and the biological response. These findings may attach importance to the effects of K+ level on Cd2+ assimilation by M. aeruginosa and shed a degree of light on the enhanced Cd2+ removal using algal-based technology.

Long-term pollutant removal performance and mitigation of rainwater quality deterioration with ceramsite and Cyperus alternifolius in mountainous cities of China.

Rainwater harvesting brings various desired environmental and social benefits in urban development. Tanks in rainwater harvesting systems need low-maintenance and low-cost approaches to manage water quality, especially for scattered small rainwater tanks associated with complex terrains in mountainous cities. Four rain barrels were set up to store roof runoff at the campus of Chongqing University, Chongqing, China. Barrel 1 (B1) and barrel 2 (B2) stored the first-flush water and the roof runoff with first-flush water diverted, respectively, while barrel 3 (B3) was loaded with a biological ceramsite and barrel 4 (B4) used biological ceramsite as a substrate media and planted with Cyperus alternifolius (C. alternifolius) to treat the first-flush water. The performances of the rain barrels were evaluated as well as the variations in water quality parameters were examined. The removal efficiency of B3 was 48.2%, 76.0%, 44.3%, and 24.6% for COD, NH4+-N, TN, and TP, respectively, while B4 had removal efficiencies of 93.4%, 71.0%, 75.0%, and 76.5% for COD, NH4+-N, TN, and TP, respectively. B4 had BOD, NH4+-N, TN, and TP concentrations within the class III Chinese Standard requirement after a storage period of about 240 days. Furthermore, the turbidity in B4 kept dropping. Thus, B4 is a more promising alternative for water quality management in mountainous cities of China.

Using multivariate techniques to assess the effects of urbanization on surface water quality: a case study in the Liangjiang New Area, China.

Rapid urbanization in China has been causing dramatic deterioration in the water quality of rivers and threatening aquatic ecosystem health. In this paper, multivariate techniques, such as factor analysis (FA) and cluster analysis (CA), were applied to analyze the water quality datasets for 19 rivers in Liangjiang New Area (LJNA), China, collected in April (dry season) and September (wet season) of 2014 and 2015. In most sampling rivers, total phosphorus, total nitrogen, and fecal coliform exceeded the Class V guideline (GB3838-2002), which could thereby threaten the water quality in Yangtze and Jialing Rivers. FA clearly identified the five groups of water quality variables, which explain majority of the experimental data. Nutritious pollution, seasonal changes, and construction activities were three key factors influencing rivers' water quality in LJNA. CA grouped 19 sampling sites into two clusters, which located at sub-catchments with high- and low-level urbanization, respectively. One-way ANOVA showed the nutrients (total phosphorus, soluble reactive phosphorus, total nitrogen, ammonium nitrogen, and nitrite), fecal coliform, and conductivity in cluster 1 were significantly greater than in cluster 2. Thus, catchment urbanization degraded rivers' water quality in Liangjiang New Area. Identifying effective buffer zones at riparian scale to weaken the negative impacts of catchment urbanization was recommended.

The ecological filter system for treatment of decentralized wastewater.

A vertical flow constructed wetland was combined with a biological aerated filter to develop an ecological filter, and to obtain the optimal operating parameters: The hydraulic loading was 1.55 m3/(m2·d), carbon-nitrogen ratio was 10, and gas-water ratio was 6. The experimental results demonstrated considerable removal efficiency of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP) in wastewater by the ecological filter, with average removal rates of 83.79%, 93.10%, 52.90%, and 79.07%, respectively. Concentration of NH4+-N after treatment met the level-A discharge standard of GB18918-2002. Compared with non-plant filter, the ecological filter improved average removal efficiency of COD, NH4+-N, TN, and TP by 13.03%, 25.30%, 14.80%, and 2.32%, respectively: thus, plants significantly contribute to the removal of organic pollutants and nitrogen. Through microporous aeration and O2 secretion of plants, the ecological filter formed an aerobic-anaerobic-aerobic alternating environment; thus aerobic and anaerobic microbes were active and effectively removed organic pollutants. Meanwhile, nitrogen and phosphorus were directly assimilated by plants and as nutrients of microorganisms. Meanwhile, pollutants were removed through nitrification, denitrification, filtration, adsorption, and interception by the filler. High removal rates of pollutants on the ecological filter proved that it is an effective wastewater-treatment technology for decentralized wastewater of mountainous towns.