Role of phosphate in microalgal-bacterial symbiosis system treating wastewater containing heavy metals.

Phosphorus is one of the important factors to successfully establish the microalgal-bacterial symbiosis (MABS) system. The migration and transformation of phosphorus can occur in various ways, and the effects of phosphate on the MABS system facing environmental impacts like heavy metal stress are often ignored. This study investigated the roles of phosphate on the response of the MABS system to zinc ion (Zn2+). The results showed that the pollutant removal effect in the MABS system was significantly reduced, and microbial growth and activity were inhibited with the presence of Zn2+. When phosphate and Zn2+ coexisted, the inhibition effects of pollutants removal and microbial growth rate were mitigated compared to that of only with the presence of Zn2+, with the increasing rates of 28.3% for total nitrogen removal, 48.9% for chemical oxygen demand removal, 78.3% for chlorophyll-a concentration, and 13.3% for volatile suspended solids concentration. When phosphate was subsequently supplemented in the MABS system after adding Zn2+, both pollutants removal efficiency and microbial growth and activity were not recovered. Thus, the inhibition effect of Zn2+ on the MABS system was irreversible. Further analysis showed that Zn2+ preferentially combined with phosphate could form chemical precipitate, which reduced the fixation of MABS system for Zn2+ through extracellular adsorption and intracellular uptake. Under Zn2+ stress, the succession of microbial communities occurred, and Parachlorella was more tolerant to Zn2+. This study revealed the comprehensive response mechanism of the co-effects of phosphate and Zn2+ on the MABS system, and provided some insights for the MABS system treating wastewater containing heavy metals, as well as migration and transformation of heavy metals in aquatic ecosystems.

Revealing mechanisms of triclosan on the removal and distribution of nitrogen and phosphorus in microalgal-bacterial symbiosis system.

Microalgal-bacterial symbiosis (MABS) system performs synergistic effect on the reduction of nutrients and carbon emissions in the water treatment process. However, antimicrobial agents are frequently detected in water, which influence the performance of MABS system. In this study, triclosan (TCS) was selected to reveal the effects and mechanisms of antimicrobial agents on MABS system. Results showed that the removal efficiencies of chemical oxygen demand, NH4+-N and total phosphorus decreased by 3.0%, 24.0% and 14.3% under TCS stress. In contrast, there were no significant decrease on the removal effect of total nitrogen. Mechanism analysis showed that both the growth rate of microorganisms and the nutrients retention capacity of extracellular polymeric substances were decreased. The intracellular accumulation for nitrogen and phosphorus was promoted due to the increased cytomembrane permeability caused by lipid peroxidation. Moreover, microalgae were dominant in MABS system with ratio between microalgae and bacteria of more than 5.49. The main genus was Parachlorella, with abundance of more than 90%. Parachlorella was highly tolerant to TCS, which might be conductive to maintain its survival. This study revealed the nutrients pathways of MABS system under TCS stress, and helped to optimize the operation of MABS system.

Role of extracellular polymeric substances on nutrients storage and transfer in algal-bacteria symbiosis sludge system treating wastewater.

This study reported the role and significance of extracellular polymeric substances (EPSs) on nutrients storage and transfer in an algal-bacteria symbiosis sludge (ABSS) system for wastewater treatment, and the novel algae-based sequencing batch suspended biofilm reactor (A-SBSBR, Ra) was selected as model of ABSS system. Results showed that compared to conventional SBSBR, the EPS of Ra performed better storage for NO2--N, NO3--N, total phosphorus and PO43- -P, with increase ratios of 43.7%, 36.0%, 34.1% and 14.7% in sludge phase and 174.0%, 147.4%, 150.4% and 122.0% in biofilm phase, respectively. The analysis of mechanisms demonstrated that microalgae active transport and uptake for divalent cations could enhance their local concentrations around ABS flocs and partially neutralized negative charge of EPSs, and more anions related to nutrients were absorbed in EPSs. Moreover, O2 produced by microalgae photosynthesis enhanced bacteria activity and improved the production of EPSs in both sludge and biofilm phases.

Insight into nitrogen and phosphorus coupling effects on mixotrophic Chlorella vulgaris growth under stably controlled nutrient conditions.

In water environment, nitrogen (N) and phosphorus (P) are biochemically dependent nutrients following the co-limitation concept for algae growth under mixotrophic mode. From a practical viewpoint, algae growth may not bring about significant change of the background nutrient concentration of an actual waterbody in contrast to a conventional batch system. In order to better understand the growth pattern of microalgae in aquatic environments, a series of experiments were conducted under stably controlled N-P levels for studying the N-P coupling effect on mixotrophic Chlorella vulgaris growth process, with attention paid to the physiological and biochemical characteristics. It was found that within the concentration range of N = 1-8 mg·L-1 and P = 0.1-1.0 mg·L-1, the variation of the N-P level slightly affected the specific growth rate, but significantly influenced nutrients uptake, biomass dry weight, chlorophyll contents of the grown C. vulgaris. The biochemical and elemental composition of the microalgae tended to be more sensitive to the N-P concentrations and ratios in the lower nutrient range (1-2 mg N·L-1, 0.1-0.4 mg P·L-1) in which the highest N and P conversion rates were gained as 90.18 ± 1.23% and 60.47 ± 1.59%, respectively. The P assimilation and conversion efficiencies were much affected by both N and P supplies, while the P supply showed little influence on N assimilation and conversion efficiencies. It was also noticed that the N level greatly affected the metabolic pathway involving nutrient assimilation, carbohydrate fixation and monosaccharide profile, resulting in conversion of the dominant fraction of protein at N ≤ 2 mg·L-1 into other biochemical compositions including lipids at N ≥ 3 mg·L-1. The fatty acid methyl esters (FAMEs) composition tended to differ with varied nutrient levels. These findings may deepen our understanding of algal growth in aquatic environment and provide perspective for eutrophication control.

Effects of plants competition on critical bacteria selection and pollutants dynamics in a long-term polyculture constructed wetland.

The effects of mix planting on the functions of plants, microorganisms, and their interactions were studied in a CW planted with Phragmites australis and Typha orientalis over six years. Findings show notable competition among plant species, with excessive overgrowth of the dominant species (P. australis) over T. orientalis. The excessive outcompeting by P. australis resulted in significantly higher plant density and biomass of 20.1 times and 11.2 times, respectively than that of T. orientalis. Interspecific competition appeared to considerably intensify plants contributions to nitrogen and phosphorus removal, which increased from circa 9% in the first year up to 42% in the sixth year. High-throughput pyrosequencing and network analyses demonstrated that the dominant species stands harbor diverse bacterial communities that could enhance the wetland performance through carbon degradation, nutrient cycling, and supporting plant growth. These results provide useful insights into the interactive effects of plants and bacteria in polyculture constructed wetlands.

Effect of additional food waste slurry generated by mesophilic acidogenic fermentation on nutrient removal and sludge properties during wastewater treatment.

Fermentation slurry from food waste (FSFW) generated by acidogenic fermentation at mesophilic temperature was utilized to improve the nutrients removal from wastewater. Organic acids (such as lactate and volatile fatty acids) in the FSFW behaved as readily biodegradable carbon sources, while the particulate and macromolecular organics acted as slowly biodegradable carbon sources during denitrification processes. The FSFW dosage significantly influenced the nitrogen removal performance, and a C/N ratio (in terms of chemical oxygen demand to nitrogen ratio) of 8 could achieve complete denitrification in the batch tests. In a sequencing batch reactor (SBR) using FSFW for long-term wastewater treatment, extracellular polymeric substances (EPS) gradually accumulated, sludge particle size significantly increased, and microbial communities were selectively enriched, which contributed to promoting the nitrogen (>80%) and phosphate (90.1%) removal efficiencies. Overall, the FSFW produced by acidogenic fermentation under mesophilic temperature served as an excellent intermediary between FW valorization and wastewater treatment.

Characterization and evolution of antibiotic resistance of Salmonella in municipal wastewater treatment plants.

The objective of this study was to investigate the evolution of antibiotic resistance phenotypes, antibiotic resistance genes (ARGs) and Class 1 integron of Salmonella in municipal wastewater treatment plants (WWTPs). A total of 221 Salmonella strains were isolated from different stages of three WWTPs. After the susceptibility testing, high frequency of resistance was observed for tetracycline (TET, 47.5% of isolates) and sulfamethoxazole (SMZ, 38.5%), followed by ampicillin (AMP, 25.3%), streptomycin (STP, 17.6%), chloramphenicol (CHL, 15.4%), and gentamicin (GEN, 11.3%). Low prevalence of resistance was detected for norfloxacin (0.45%), ciprofloxacin (0.9%), and cefotaxime (0.9%). The tetA and sul3 genes were most frequently detected among the Salmonella isolates. Statistically significant correlations among AMP, CHL, GEN, and STP resistances were observed. High detection frequencies of Class 1 integron were observed in double antibiotic-resistant and multiple-antibiotic-resistant (MAR) Salmonella, which were 94.3% and 85.7%, respectively. The proliferation of MAR Salmonella and transfer of ARGs occurred in WWTPs. Class 1 integron plays a crucial role in the evolution of MAR Salmonella during WWTPs.

Bioretention cell incorporating Fe-biochar and saturated zones for enhanced stormwater runoff treatment.

Nitrogen (N) and phosphorus (P) removal in conventional bioretention systems is highly variable. Therefore, five novel experimental columns with different media configurations and constituents, and incorporating a saturated zone were developed and assessed to optimize the removal of N, P and other nutrients. Three types of media composed of the conventional mixed sand and soil media (T1), biochar-amended media (T2), and iron-coated biochar (ICB)-amended media (T3) were evaluated. Two of the experimental columns were designed with double-layer configurations, while the other three were of a single-layer structure. Removal efficiencies of nutrients in the experimental columns were evaluated and compared using simulated runoff. Also, the effect of media depth on the retention of P and denitrifying enzyme activity (DEA) in the bioretention columns were evaluated. The experimental column only filled with T3 showed the best performance for COD, ammonia (NH4+-N) and total phosphorus (TP) removal (94.6%, 98.3% and 93.70%, respectively), whereas columns filled with T2 performed poorly for TP removal (57.36%). For the removal of nitrate (NO3--N) and total nitrogen (TN), the columns using a single-layer and only filled with either T3 or T2 exhibited the best performance (93% and 97% TN removal, respectively). Overall, this study demonstrates that our proposed single-layered bioretention cell only filled with T3 and incorporating a saturated zone effectively improves the runoff quality, and can provide a new bioretention cell configuration for efficient stormwater treatment.

Nutrients removal performance and sludge properties using anaerobic fermentation slurry from food waste as an external carbon source for wastewater treatment.

Enhancement of nitrogen and phosphate removal using thermophilic fermentation slurry from food waste (FSFW) as external carbon source was investigated. Based on the batch tests, the soluble and particulate fractions of the FSFW acted as easily and slowly biodegradable carbon sources, respectively, and the fermented slurry showed the combined nutrients removal properties of soluble and solid organics. During the long-term operation of a sequencing batch reactor (SBR) with FSFW for wastewater treatment, the sludge particle size increased obviously, the bacterial metabolic capacity improved significantly, and some functional microorganisms were enriched selectively, which significantly promoted the nitrogen removal efficiency (approximately 90%) by enhancing the anoxic denitrification and simultaneous nitrification and denitrification (SND) processes. Moreover, high phosphate removal efficiency (above 98%) was achieved through the aerobic and anoxic phosphate accumulation processes. Thus, using the FSFW as supplementary carbon source is a suitable solution for both food waste disposal and wastewater treatment.

Functional evaluation of pollutant transformation in sediment from combined sewer system.

In this study, a pilot combined sewer system was constructed to characterize the pollutant transformation in sewer sediment. The results showed that particulate contaminants deposited from sewage could be transformed into dissolved matter by distinct pollutant transformation pathways. Although the oxidation-reduction potential (ORP) was varied from -80 mV to -340 mV in different region of the sediment, the fermentation was the dominant process in all regions of the sediment, which induced hydrolysis and decomposition of particulate contaminants. As a result, the accumulation of dissolved organic matter and the variation of ORP values along the sediment depth led to the depth-dependent reproduction characteristics of methanogens and sulfate-reducing bacteria, which were existed in the middle and deep layer of the sediment respectively. However, the diversity of nitrifying and polyphosphate-accumulating bacteria was low in sewer sediment and those microbial communities showed a non-significant correlation with nitrogen and phosphorus contaminants, which indicated that the enrichment of nitrogen and phosphorus contaminants was mainly caused by physical deposition process. Thus, this study proposed a promising pathway to evaluate pollutant transformation and can help provide theoretical foundation for urban sewer improvement.

On the risks from sediment and overlying water by replenishing urban landscape ponds with reclaimed wastewater.

The extensive use of reclaimed wastewater (RW) as a source of urban landscape pond replenishment, stimulated by the lack of surface water (SW) resources, has raised public concern. Greater attention should be paid to pond sediments, which act as 'sinks' and 'sources' of contaminants to the overlying pond water. Three ponds replenished with RW (RW ponds) in three Chinese cities were chosen to investigate 22 indices of sediment quality in four categories: eutrophication, heavy metal, ecotoxicity and pathogens risk. RW ponds were compared with other ponds of similar characteristics in the same cities that were replenished with SW (SW ponds). Our results show a strong impact of RW to the eutrophication and pathogenic risks, which are represented by organic matter, water content, total nitrogen, total phosphorus and phosphorus fractions, and pathogens. In particular, total phosphorus concentrations in the RW pond sediments were, on average, 50% higher than those of SW ponds. Moreover, the content of phosphorus, extracted by bicarbonate/dithionite (normally represented by BD-P) and NaOH (NaOH-P), were 2.0- and 2.83-times higher in RW ponds, respectively. For pathogens, the concentrations of norovirus and rotavirus in RW pond sediments were, on average, 0.52 and 0.30- log times those of SW ponds. The duration of RW replenishment was proved to have a marked impact on the eutrophication and pathogens risks from sediments. The continued use of RW for replenishment increases the eutrophication risk, and the pathogens risk, especially by viral pathogens, becomes greater.

New thermodynamic entropy calculation based approach towards quantifying the impact of eutrophication on water environment.

Although the eutrophication phenomenon has been studied for a long time, there are still no quantifiable parameters available for a comprehensive assessment of its impacts on the water environment. As contamination alters the thermodynamic equilibrium of a water system to a state of imbalance, a novel method was proposed, in this study, for its quantitative evaluation. Based on thermodynamic analyses of the algal growth process, the proposed method targeted, both theoretically and experimentally, the typical algae species encountered in the water environment. By calculating the molar enthalpy of algae biomass production, the heat energy dissipated in the photosynthetic process was firstly evaluated. The associated entropy production (ΔS) in the aquatic system could be then obtained. For six algae strains of distinct molecular formulae, the heat energy consumed for the production of a unit algal biomass was found to proportionate to the mass of nitrogen (N) or phosphorus (P) uptake through photosynthesis. A proportionality relationship between ΔS and the algal biomass with a coefficient circa 44kJ/g was obtained. By the principle of energy conservation, the heat energy consumed in the process of algae biomass production is stored in the algal biomass. Furthermore, by measuring the heat of combustion of mature algae of Microcystis flos-aquae, Anabaena flos-aquae, and Chlorella vulgaris, the proportionality relationships between the heat energy and the N and P contents were validated experimentally at 90% and 85% confidence levels, respectively. As the discharge of excess N and P from domestic wastewater treatment plants is usually the main cause of eutrophication, the proposed impact assessment approach estimates that for a receiving water body, the ΔS due to a unit mass of N and P discharge is 268.9kJ/K and 1870.1kJ/K, respectively. Consequently, P discharge control would be more important for environmental water protection.

Phosphorus removal from aqueous solution using a novel granular material developed from building waste.

In this study, a granular material (GM) developed from building waste was used for phosphate removal from phosphorus-containing wastewater. Batch experiments were executed to investigate the phosphate removal capacity of this material. The mechanism of removal proved to be a chemical precipitation process. The characteristics of the material and resulting precipitates, the kinetics of the precipitation and Ca2+ liberation processes, and the effects of dosage and pH were investigated. The phosphate precipitation and Ca2+ liberation processes were both well described by a pseudo-second-order kinetic model. A maximum precipitation capacity of 0.51 ± 0.06 mg g-1 and a liberation capacity of 6.79 ± 0.77 mg g-1 were measured under the experimental conditions. The processes reached equilibrium in 60 min. The initial solution pH strongly affected phosphate removal under extreme conditions (pH <4 and pH >10). The precipitates comprised hydroxyapatite and brushite. This novel GM can be considered a promising material for phosphate removal from wastewater.

Characterizing phosphorus removal from polluted urban river water by steel slags in a vertical flow constructed wetland.

Phosphorus (P) removal in constructed wetlands (CWs) is often low unless special substrates with high sorption capacities are used. However, the use of special substrates in vertical flow (VF) CWs has not been proved to enhance P sorption. Thus, two VF wetlands were designed to evaluate the potential for enhanced P removal from polluted urban river water, one with slag as substrate and the other as a control with gravel as substrate. Findings from batch experiments showed P sorption capacities of 3.15 gP/kg and 0.81 gP/kg, respectively, for steel slag and gravel. Different organic matter fractions played different roles in P sorption, the effects of which were significant only at high concentrations. Over a 220 days' operation, the VF-slag removed 76.0% of the influent total phosphorus (TP) at 0.159 g/m(2)·d and PO4-P of 70.9% at 0.063 g/m(2)·d, whereas the VF-gravel removed 65.0% at 0.136 g/m(2)·d and 48.6% at 0.040 g/m(2)·d, respectively. Therefore, the merit of using a steel slag substrate in VF wetlands can be significant for the removal of PO4-P.

New functional biocarriers for enhancing the performance of a hybrid moving bed biofilm reactor-membrane bioreactor system.

In this study, new sponge modified plastic carriers for moving bed biofilm reactor (MBBR) was developed. The performance and membrane fouling behavior of a hybrid MBBR-membrane bioreactor (MBBR-MBR) system were also evaluated. Comparing to the MBBR with plastic carriers (MBBR), the MBBR with sponge modified biocarriers (S-MBBR) showed better effluent quality and enhanced nutrient removal at HRTs of 12h and 6h. Regarding fouling issue of the hybrid systems, soluble microbial products (SMP) of the MBR unit greatly influenced membrane fouling. The sponge modified biocarriers could lower the levels of SMP in mixed liquor and extracellular polymeric substances in activated sludge, thereby mitigating cake layer and pore blocking resistances of the membrane. The reduced SMP and biopolymer clusters in membrane cake layer were also observed. The results demonstrated that the sponge modified biocarriers were capable of improving overall MBBR performance and substantially alleviated membrane fouling of the subsequent MBR unit.

Performance of a pilot demonstration-scale hybrid constructed wetland system for on-site treatment of polluted urban river water in Northwestern China.

Hybrid constructed wetland (HCW) systems have been used to treat various wastewaters across the world. However, large-scale applications of HCWs are scarce, particularly for on-site improvement of the water quality of highly polluted urban rivers in semi-arid regions. In this study, a large pilot-scale HCW system was constructed to improve the water quality of the Zaohe River in Xi'an, China. With a total area of about 8000 m(2), the pilot HCW system, composed of different configurations of surface and subsurface flow wetlands, was operated for 2 years at an average inflow volume rate of 362 m(3)/day. Local Phragmites australis and Typha orientalis from the riverbank were planted in the HCW system. Findings indicate a higher treatment efficiency for organics and suspended solids than nutrients. The inflow concentrations of 5-day biochemical oxygen demand (BOD5), chemical oxygen demand (COD), suspended solids (SS), total nitrogen (TN), NH3-N, and total phosphorus (TP) were 125.6, 350.9, 334.2, 38.5, 27.2, and 3.9 mg/L, respectively. Average removal efficiencies of 94.4, 74.5, 92.0, 56.3, 57.5, and 69.2%, respectively, were recorded. However, the pollutant removal rates were highly seasonal especially for nitrogen. Higher removals were recorded for all pollutants in the autumn while significantly lower removals were recorded in the winter. Plant uptake and assimilation accounted for circa 19-29 and 16-23% of the TN and TP removal, respectively. Moreover, P. australis demonstrated a higher nutrient uptake ability and competitive potential. Overall, the high efficiency of the pilot HCW for improving the water quality of such a highly polluted urban river provided practical evidence of the applicability of the HCW technology for protecting urban water environments.

Impact assessment of excess discharges of organics and nutrients into aquatic systems by thermodynamic entropy calculation.

In this study, a method was proposed for calculating the thermodynamic entropy increase ΔS in a water body after receiving excess discharge of organics and nutrients in order to quantitatively assess the impact of pollutants discharge on aquatic systems. The enthalpy change was evaluated using the standard thermodynamic data according to the possible chemical and/or biochemical reactions such as organic oxidation, nitrification/denitrification, and phosphorus precipitation, for the recovery of water quality to the background level. A series of equations were established for calculating the ΔS associated with the decomposition or removal of TOC, NO(3)-N, NO(2)-N, NH(3)-N and TP. The values of ΔS corresponding to unit mass (per g) of these pollutants were calculated as 54.0 kJ/K, 2.91 kJ/K, 10.01 kJ/K, 28.51 kJ/K and 2.81 kJ/K, respectively. Besides, the applicability of the proposed method was proved by a scenario analysis regarding effluent quality control and surface water quality protection in China.