Chenxi Wu

Advanced nutrient removal from surface water by a consortium of attached microalgae and bacteria: A review

Innovative and cost-effective technologies for advanced nutrient removal from surface water are urgently needed for improving water quality. Conventional biotechnologies, such as ecological floating beds, or constructed wetlands, are not effective in removing nutrients present at low-concentration. However, microalgae-bacteria consortium is promising for advanced nutrient removal from wastewater. Suspended algal-bacterial systems can easily wash out unless the hydraulic retention time is long, attached microalgae-bacteria consortium is more realistic. This critical review summarizes the fundamentals and status of attached microalgae-bacteria consortium for advanced nutrient removal from surface water. Key advantages are the various nutrient removal pathways, reduction of nutrients to very low concentration, and diversified photobioreactor configurations. Challenges include poor identification of functional species, poor control of the community composition, and long start-up times. Future research should focus on the selection and engineering of robust microbial species, mathematical modelling of the composition and functionality of the consortium, and novel photobioreactor configurations.

Sources and distribution of microplastics in China's largest inland lake - Qinghai Lake

Microplastic pollution was studied in Chinas largest inland lake - Qinghai Lake in this work. Microplastics were detected with abundance varies from 0.05u202f×u202f105 to 7.58u202f×u202f105 items km-2 in the lake surface water, 0.03u202f×u202f105 to 0.31u202f×u202f105 items km-2 in the inflowing rivers, 50 to 1292 items m-2 in the lakeshore sediment, and 2 to 15 items per individual in the fish samples, respectively. Small microplastics (0.1-0.5u202fmm) dominated in the lake surface water while large microplastics (1-5u202fmm) are more abundant in the river samples. Microplastics were predominantly in sheet and fiber shapes in the lake and river water samples but were more diverse in the lakeshore sediment samples. Polymer types of microplastics were mainly polyethylene (PE) and polypropylene (PP) as identified using Raman Spectroscopy. Spatially, microplastic abundance was the highest in the central part of the lake, likely due to the transport of lake current. Based on the higher abundance of microplastics near the tourist access points, plastic wastes from tourism are considered as an important source of microplastics in Qinghai Lake. As an important area for wildlife conservation, better waste management practice should be implemented, and waste disposal and recycling infrastructures should be improved for the protection of Qinghai Lake.

Using the Asian clam as an indicator of microplastic pollution in freshwater ecosystems

Bioindicators play an important role in understanding pollution levels, bioavailability and the ecological risks of contaminants. Several bioindicators have been suggested for understanding microplastic in the marine environment. A bioindicator for microplastics in the freshwater environment does not exist. In our previous studies, we found a high frequency of microplastic pollution in the Asian clam (Corbicula fluminea) in Taihu Lake, China. In the present study, we conducted a large-scale survey of microplastic pollution in Asian clams, water and sediment from 21 sites in the Middle-Lower Yangtze River Basin from August to October of 2016. The Asian clam was available in all sites, which included diverse freshwater systems such as lakes, rivers and estuaries. Microplastics were found at concentrations ranging from 0.3-4.9 items/g (or 0.4-5.0 items/individual) in clams, 0.5-3.1 items/L in water and 15-160 items/kg in sediment. Microfibers were the most dominant types of microplastics found, accounting for 60-100% in clams across all sampling sites. The size of microplastics ranged from 0.021-4.83xa0mm, and microplastics in the range of 0.25-1xa0mm were dominant. The abundance, size distribution and color patterns of microplastics in clams more closely resembled those in sediment than in water. Because microplastic pollution in the Asian clam reflected the variability of microplastic pollution in the freshwater environments, we demonstrated the Asian clam as an bioindicator of microplastic pollution in freshwater systems, particularly for sediments.

Responses of Periphyton to Fe2O3 Nanoparticles: A Physiological and Ecological Basis for Defending Nanotoxicity

The toxic effects of nanoparticles on individual organisms have been widely investigated, while few studies have investigated the effects of nanoparticles on ubiquitous multicommunity microbial aggregates. Here, periphyton as a model of microbial aggregates, was employed to investigate the responses of microbial aggregates exposed continuously to Fe2O3 nanoparticles (5.0 mg L-1) for 30 days. The exposure to Fe2O3 nanoparticles results in the chlorophyll (a, b, and c) contents of periphyton increasing and the total antioxidant capacity decreasing. The composition of the periphyton markedly changes in the presence of Fe2O3 nanoparticles and the species diversity significantly increases. The changes in the periphyton composition and diversity were due to allelochemicals, such as 3-methylpentane, released by members of the periphyton which inhibit their competitors. The functions of the periphyton represented by metabolic capability and contaminant (organic matter, nitrogen, phosphorus and copper) removal were able to acclimate to the Fe2O3 nanoparticles exposure via self-regulation of morphology, species composition and diversity. These findings highlight the importance of both physiological and ecological factors in evaluating the long-term responses of microbial aggregates exposed to nanoparticles.

Periphyton biofilm development and its role in nutrient cycling in paddy microcosms

PurposePeriphyton exists commonly in paddy field but its characteristics and role in nutrient cycling are poorly understood. In this work, microcosm experiments were carried out for 6xa0weeks to study the development and succession of periphyton in paddy soil and to evaluate the roles of periphyton in N and P cycling in the rice paddy system.Materials and methodsThe development and role of periphyton was investigated using microcosms prepared from paddy soil from the field with and without fertilization. Nutrient levels in water, periphyton layer, and soil layers were monitored overtime. Total nitrogen (TN), ammonia, nitrate, total phosphorous (TP), soluble reactive phosphorus (SRP), and pH were analyzed in water. Periphyton samples were analyzed for chlorophyll a, total Kjeldahl nitrogen (TKN), TP, and P fractionation, and DNA was extracted for Hiseq sequencing. Upper and lower soil samples were only analyzed for TKN and TP.Results and discussionDevelopment of periphyton was observed on the soil/water interface with or without the addition of fertilizer and caused an increase in water pH. In both treatments, nutrient levels declined rapidly overtime in the first few weeks but gradually slowed down toward the end of the experiment. Hiseq sequencing showed a considerable variation of microbial community in periphyton over time in both treatments. For algae, fertilization resulted in an increase in the relative abundance of Chlorophyta, but as nutrient became deficient Diatomea became dominant. For prokaryotes, Chloroflexi was dominated in the initial and former growth phases, while Cyanobacteria dominated the latter growth and mature phases regardless of nutrient levels.ConclusionsPeriphyton can develop on the interface of soil and water in paddy system regardless of the nutrient status. Its microbial compositions can vary overtime and are related to the nutrient levels. Presence of periphyton accelerates the nutrient removal from overlaying water although the removal was rapid even without periphyton.

Microplastic pollution in China's inland water systems: A review of findings, methods, characteristics, effects, and management

The pollution of marine environments and inland waters by plastic debris has raised increasing concerns worldwide in recent years. China is the worlds largest developing country and the largest plastic producer. In this review, we gather available information on microplastic pollution in Chinas inland water systems. The results show that microplastics are ubiquitous in the investigated inland water systems, and high microplastic abundances were observed in developed areas. Although similar sampling and analytical methods were used for microplastic research in inland water and marine systems, methods of investigation should be standardized in the future. The characteristics of the detected microplastics suggest secondary sources as their major sources. The biological and ecological effects of microplastics have been demonstrated, but their risks are difficult to determine at this stage due to the discrepancy between the field-collected microplastics and microplastics used in ecotoxicological studies. Although many laws and regulations have already been established to manage and control plastic waste in China, the implementation of these laws and regulations has been ineffective and sometimes difficult. Several research priorities are identified, and we suggest that the Chinese government should be more proactive in tackling plastic pollution problems to protect the environment and fulfill international responsibilities.

Influence of light and temperature on the development and denitrification potential of periphytic biofilms

Periphytic biofilms are microbial aggregates commonly present in submerged aquatic environments and play a significant role in nutrient cycling. In recent years, utilization of natural periphytic biofilms in wastewater treatment and water restoration attracts growing research interests. Light and temperature are two important environmental factors known to affect the development of periphytic biofilms and can be manipulated for the regulation of the biofilm properties. In this work, effects of light and temperature on the development and function (denitrification potential) of periphytic biofilms were investigated using a microcosm experiment. Results showed that thicker periphytic biofilms with higher Chlorophyll a, extracellular polymeric substances (EPS), and total phosphorus contents were developed under higher temperature. Whereas, biomass accumulation was more rapid for periphytic biofilms under higher irradiance. The denitrification potential rate was negatively associated with irradiance, which can be linked to the influence of irradiance on biofilm structure and microbial composition. A relatively lower irradiance is recommended when using periphytic biofilms in nitrogen removal from wastewater.

Removal of nutrients and pharmaceuticals and personal care products from wastewater using periphyton photobioreactors

In this work, periphyton photobioreactors were built and were used for the treatment of synthetic wastewater spiked with PPCPs under different operational conditions. The removal rates of total nitrogen were relatively stable and varied from 39% to 77% overtime in different treatments. However, the removal rates of soluble reactive phosphorus decreased overtime from 42% to 68% on day 2 to 15.8% to 44% on day 22. For the selected PPCPs, only bisphenol A was effectively removed (72%-86.4%), hydrochlorothiazide and ibuprofen were moderately removed (26.2%-48.7%), and carbamazepine and gemfibrozil were poorly removed (6.45%-20.6%). Longer hydraulic retention time enhanced the treatment efficiency but illumination period showed contrasting effects on the removal of the nutrients and the PPCPs.

The counter-balance between ammonia absorption and the stimulation of volatilization by periphyton in shallow aquatic systems

Ammonia (NH3) volatilization is one of the main pathways of nitrogen (N). The aim of this work was to investigate the determinants of NH3 volatilization, and characterize how the overlying water, sediment, and periphyton interact to regulate the rates of NH3 volatilization in shallow aquatic systems. Two types of structural equation modeling (SEM) methods (elements and components models) were evaluated to examine the complex multivariate response of NH3 volatilization. The N components and the pH in the elements models exerted significant and positive effects on NH3 volatilization. The water column accounted for the greatest variation of NH3 volatilization in a favorable pH environment and high NH4+-N concentrations according to the components models. Although periphyton biofilm prohibited the direct flow of NH3 gas, this was counter-balanced by its indirect stimulation effects that positively affected the NH4+-N and DOC concentrations and the pH in both the overlying water and the sediment.

Removal of pharmaceuticals and personal care products from wastewater using algae-based technologies: a review

Pharmaceuticals and personal care products (PPCPs) consist of a variety of compounds extensively used for the treatment of human and animal diseases and for health or cosmetic reasons. PPCPs are considered as emerging environmental contaminants due to their ubiquitous presence in the environment and high environmental risks. In wastewater treatment plants using conventional activated sludge processes, many PPCPs cannot be efficiently removed. Therefore, there is an increasing need for more effective and cost-efficiency ways of removing PPCPs while treating wastewater. Algae-based technologies have recently attracted growing attentions for their potential application in wastewater treatment and hazardous contaminant removal, which are advantages in reducing operation cost while generating valuable products and sequestrating greenhouse gases at the same time. This work reviews the up-to date researches to reveal potential toxic effects of PPCPs on algae and algae-bacteria consortia, identify mechanisms involved in PPCP removal, and assess the fate of PPCPs in algae-based treatment systems. Current researches suggest that algae and algae-bacteria consortia have great potentials in PPCP removal but more works are required before algae-based technologies can be implemented in large scales. Knowledge gaps are identified and further research focuses are proposed in this review.