Junzhuo Liu

Differences in nutrient uptake capacity of the benthic filamentous algae Cladophora sp., Klebsormidium sp. and Pseudanabaena sp. under varying N/P conditions

The N/P ratio of wastewater can vary greatly and directly affect algal growth and nutrient removal process. Three benthic filamentous algae species Cladophora sp., Klebsormidium sp. and Pseudanabaena sp. were isolated from a periphyton bioreactor and cultured under laboratory conditions on varying N/P ratios to determine their ability to remove nitrate and phosphorus. The N/P ratio significantly influenced the algal growth and phosphorus uptake process. Appropriate N/P ratios for nitrogen and phosphorus removal were 5-15, 7-10 and 7-20 for Cladophora sp., Klebsormidium sp. and Pseudanabaena sp., respectively. Within these respective ranges, Cladophora sp. had the highest biomass production, while Pseudanabaena sp. had the highest nitrogen and phosphorus contents. This study indicated that Cladophora sp. had a high capacity of removing phosphorus from wastewaters of low N/P ratio, and Pseudanabaena sp. was highly suitable for removing nitrogen from wastewaters with high N/P ratio.

Start-up of a spiral periphyton bioreactor (SPR) for removal of COD and the characteristics of the associated microbial community.

Periphyton-based bioreactors are widely accepted for removing various pollutants from wastewater; however, the slow start-up and low efficiency in widely fluctuating temperatures limit its application. A spiral periphyton bioreactor (SPR) was developed and its COD removal capability and the associated microbial communities were investigated. This SPR can be easily backwashed to stimulate periphyton growth and efficiently remove COD at temperatures ranging from 4 to 30 °C. The species richness and evenness of the periphyton community increased during domestication, while its functional diversity and organic carbon metabolic vitality were higher after 30 days domestication. Cyanobacteria were the main components of the SPR and produced an aerobic environment, while Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria and Sphingobacteria were the microorganisms responsible for COD removal. This study provides valuable insights into changes in pivotal microorganisms of the periphyton community during domestication, and indicates that SPR is simple to operate and efficient in COD removal.

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.

Nutrient removal by up-scaling a hybrid floating treatment bed (HFTB) using plant and periphyton: From laboratory tank to polluted river

Planted floating treatment bed (FTB) is an innovative technique of removing nutrients from polluted water but limited in deep water and cold seasons. Periphyton was integrated into FTB for a hybrid floating treatment bed (HFTB) to improve its nutrient removal capacity. To assess its potential for treating nutrient-polluted rivers, HFTB was up-scaled from 5L laboratory tanks to 350L outdoor tanks and then to a commercial-scale 900m section of polluted river. Plants and periphyton interacted in HFTB with periphyton limiting plant root growth and plants having shading effects on periphyton. Non-overlapping distribution of plants and periphyton can minimize the negative interactions in HFTB. HFTB successfully kept TN and TP of the river at less than 2.0 and 0.02mgL(-1), respectively. This study indicates that HFTB can be easily up-scaled for nutrients removal from polluted rivers in different seasons providing a long-term, environmentally-friendly method to remediate polluted ecosystems.

Bioremediation of agricultural solid waste leachates with diverse species of Cu (II) and Cd (II) by periphyton.

The aim of this work was to study the bioremediation of agricultural solid waste leachates with high-concentrations of Cu (II) and Cd (II) after washing the wastes with water and Na2EDTA solution (0.2M). Results indicate that Cu (II) and Cd (II) are mainly comprised of Cu2(OH)22+, Cu3(OH)42+, CuOH+, Cu(H2O)4(OH)2, Cd2+ and CdOH+ in the water-washed leachates and Cu(EDTA)2-, Cu(HEDTA)-, Cd(EDTA)2- and Cd(HEDTA)- in the Na2EDTA-washed leachates. Cu (II) removal efficiency by selected native periphyton from the water- and Na2EDTA-washed leachates were 80.5% and 68.4% respectively, and for Cd (II) it was 57.1% and 64.6%, because the periphyton was able to maintain a stable pH of the leachates and regulate its microbial composition and carbon metabolic capability to acclimate the chemical conditions of the leachates. This study provides a new biomeasure to treat leachates with high-concentration Cu2+ and Cd2+, and contribute valuable insights into the relationships between periphyton characteristics and heavy metals.

Redox zones stratification and the microbial community characteristics in a periphyton bioreactor

Bioremediation techniques based on microorganisms have been widely applied to treat polluted surface water, but the efficiencies have been limited, especially in deep and static waters. Microbial aggregates, known as periphyton, were introduced into a tank bioreactor to improve pollutants removal and a periphyton bioreactor with an 84 cm column was built to investigate microbe-wastewater interactions. Periphyton greatly improved water quality and produced a distinct stratification in the water column into five redox zones with slight overlaps. From top to bottom these were: oxygen reduction, nitrate reduction, iron reduction, sulfate reduction and methanogenic zone. Periphyton communities had high species diversities (767-947 OTUs) with the facultative zone (middle layer) having higher species richness and functional diversity than the aerobic (top layer) and anaerobic zones (bottom layer). A good knowledge of interactions between periphyton and water column stratification could benefit from integration of periphyton to improve bioremediation of deep and static water.

Fatty acid profiles of four filamentous green algae under varying culture conditions.

Although benthic filamentous algae are interesting targets for wastewater treatment and biotechnology, relatively little is known about their biochemical composition and variation in response to growth conditions. Fatty acid composition of four benthic filamentous green algae was determined in different culture conditions. Although the response was partly species-dependent, increasing culture age, nitrogen deprivation and dark exposure of stationary phase greatly increased both total fatty acid content (TFA) from 12-35 to 40-173mgg(-1) dry weight (DW) and the relative proportion of polyunsaturated fatty acids (PUFAs) from 21-58% to 55-87% of TFA, with dark exposure having the greatest effect. However, the main variation in fatty acid composition was between species, with Uronema being rich in C16:0 (2.3% of DW), Klebsormidium in C18:2ω6 (5.4% of DW) and Stigeoclonium in C18:3ω3 (11.1% of DW). This indicates the potential of the latter two species as potential sources of these PUFAs.

The effect of periphyton on seed germination and seedling growth of rice (Oryza sativa) in paddy area.

Periphyton is widely distributed in paddy fields and its interactions with paddy soil and rice growth have been reported rarely. In this study, model paddy ecosystems with different additional soil substrates were simulated under controlled conditions to investigate the effects of periphyton on rice seed germination and seedling growth. Results show that the selected soil substrates had significant effects on the metabolic activities and growth of periphyton in paddy fields. The addition of straw to soil enhances but the addition of biochar leads to attenuation of periphyton growth. The presence of periphyton in the paddy system, especially with straw in soil greatly increased the germination index of rice seed (by maximally 21%). However, the biochar treatment in the presence of periphyton was detrimental for the seed vitality with a decrease of 30%. As a result, the periphyton cover on paddy soil surface significantly inhibited the growth of rice seedling, including rice height, leaf width and biomass. To summarize, this study indicates that the presence of periphyton during seed germination period was detrimental for rice growth, but could be used to control the weed growth. Thus, this study provided insight into understanding the periphyton-plant relationships with different soil-substrates and also new approaches to controlling weeds in paddy fields by regulating the growth of periphyton.

Biosorption of high-concentration Cu (II) by periphytic biofilms and the development of a fiber periphyton bioreactor (FPBR)

In this study, a kind of microbial aggregates: periphytic biofilms were used for Cu removal and immobilized onto fiber for developing a novel bioreactor. Results show that periphyton can effectively entrap Cu at initial concentrations of 2-20mgL-1 due to the overproduction of EPS and porous structure of periphyton, and biosorption was the primary mechanism of Cu removal. Cu (mainly Cu3(OH)42+, Cu2(OH)22+ and Cu2+) adsorption onto periphytic biofilms followed the pseudo-second order kinetic model. The biosorption process fitted the Freundlich, Langmuir and Dubinin-Radushkevich Isotherm models well and was thermodynamically spontaneous. The fiber substrate used in the periphyton bioreactor greatly increased the Cation Exchange Capacity (CEC) of the system. This study indicates that immobilization of periphytic biofilms onto fiber for novel bioreactor development is a feasible way of entrapping high-concentration Cu from wastewater.

Mitigation of nonpoint source pollution in rural areas: From control to synergies of multi ecosystem services

Nonpoint source (NPS) pollution produced by human activities in rural areas has induced excessive nutrient input into surface waters and the decline of water quality. The essence of NPS pollution is the transport of nutrients between soil and water. Traditional NPS pollution control strategies, however, are mainly based on the solid and liquid phases, with little focus on the bio-phase between water and soil. The pollutants produced from NPS can be regarded as a resource if recycled or reused in an appropriate way in the agricultural ecosystem. This mini review proposes novel strategies for NPS pollution control based on three phases (liquid, solid and bio-phase) and highlights the regulating services of an agricultural ecosystem by optimizing land use/cover types.