Cyanobacterial blooms control with CaO2 in different stages: Inhibition efficiency, water quality optimization and microbial community changes.

This study explored the feasibility of calcium peroxide (CaO2) to inhibit cyanobacterial blooms of the outbreak and dormancy stages. Our previous studies have found that CaO2 has a high inhibitory effect on cyanobacteria. In order to explore the application effect of CaO2 in actual cyanobacteria lake water, we conducted this study to clarify the effect of CaO2 on inhibiting cyanobacteria in outbreak and dormancy stages. The results showed that CaO2 inhibited the growth of cyanobacteria in the outbreak and dormancy stages by 98.7% and 97.6%, respectively. The main inhibitory mechanism is: (1) destroy the cell structure and make the cells undergo programmed cell death by stimulating the oxidation balance of cyanobacteria cells; (2) EPS released by cyanobacteria resist stimulation and combine calcium to form colonies, and accelerate cell settlement. In addition to causing direct damage to cyanobacteria, CaO2 can also improve water quality and sediment microbial diversity, and reduce the release of sediment to phosphorus, so as to further contribute to cyanobacterial inhibition. Finally, the results of qRT-PCR analysis confirmed the promoting effect of CaO2 on the downregulation of photosynthesis-related genes (rbcL and psaB), microcystn (mcyA and mcyD) and peroxiredoxin (prx), and verified the mechanism of CaO2 inhibition of cyanobacteria. In conclusion, this study provides new findings for the future suppression of cyanobacterial bloom, by combining water quality, cyanobacterial inhibition mechanisms, and sediment microbial diversity.

[Preparation of Iron-improved Blue Algae Biochar and Its Co-adsorption Mechanism for Phosphorus in Surface Water].

To alleviate the problems of eutrophication and blue algae accumulation in water, biochar was prepared from blue algae dehydrated using polymerized ferrous sulfate(PFS) to absorb phosphate in water, and the biochar was activated using steam to adjust the pore structure. The preparation conditions of blue algae biochar were optimized using the response surface method. The optimal results were as follows:the dosage of PFS was 458 mg·L-1, the carbonization temperature was 433℃, and the mass ratio of biochar precursor to steam was 1:11. Biochar without PFS(F0H11-433) and biochar with PFS(F458H11-433) were characterized using X-ray diffraction(XRD), Fourier-transform infrared spectroscopy(FTIR), zeta potential, and Raman spectra(Raman) were used to study whether blue algae biochar and PFS had a synergic effect on phosphate removal. The results showed that:compared with F0H11-433, iron oxide appeared on the surface, the zero point of charge(pHpzc) increased from 4.41 to 6.19, and the disorder and defect degree of biochar was increased in F458H11-433. The pseudo-second-order model and Langmuir model were suitable for describing the adsorption process of F458H11-433, and the saturated adsorption capacity was 31.97 mg·g-1. F458H11-433 had excellent phosphorus removal efficiency in actual lake water, and the residual phosphate content of effluent was less than 0.025 mg·L-1. In the presence of several common anions, it still showed excellent selective adsorption. After five cycles, the phosphate removal of F458H11-433 still reached 75.78%, indicating that F458H11-433 had the characteristic of being renewable. Combined with the material characterization results before and after adsorption, the phosphorus removal mechanism of F458H11-433 mainly involved electrostatic attraction and ligand exchange.

Bioconversion of cyanobacteria by black soldier fly larvae (Hermetia illucens L.): Enhancement by antioxidants.

Cyanobacterial blooms have been a global environmental problem for decades. Bioconversion by black soldier fly larvae (BSFL) has been widely reported to be a clean and efficient method to remove organic pollutants. In this study, BSFL bioconversion was used to treat cyanobacterial blooms. Antioxidants (a mixture of l-ascorbic acid [180 mg/kg fresh feed] and α-tocopherol [360 mg/kg fresh feed]) were added to compare bioconversion performance against a non-supplemented group. With increasing proportions of cyanobacteria (0%-25% dry mass), the bioconversion efficiency of the antioxidant group improved significantly compared to the control group, and the survival rate of larvae rose from 96.50-45.50% to 98.00-55.83% with antioxidant addition. The toxic effects of exogenous anti-nutrients could be reduced by the antioxidants through inactivation of trypsin inhibitor and enhancement of the microcystin-LR degradation rate. Overall, the BSFL bioremediation capacity was improved with addition of exogenous antioxidants, verifying both the effects and mechanism of antioxidant addition in promoting the bioconversion of cyanobacteria by BSFL and providing a basis for future application and study.

[Restoration of River Sediment by Calcium Peroxide(CaO2) Combined with Biochar].

The internal source pollution of sediment is the main factor leading to the repetition of black-odorous river channels. In order to prevent this situation, a river channel in the Binhu District of Wuxi City was used as an experimental site. In-situ CaO2 combined with a biochar covering technology was used to repair the black odorous river sediment in this channel. The effects of this technology on the quality of mud water, sedimentary volatile sulfide (AVS) and phosphorus forms, microorganisms, and restoration of black odorous sediment were investigated. The results showed that CaO2 combined with biochar coverage could significantly increase the dissolved oxygen (DO) concentration and redox potential (ORP) of the muddy water system. The DO concentration and ORP in the overlying water were maintained above 2 mg·L-1 and 50 mV, respectively. The removal rates of interstitial water ammonia-nitrogen (NH4+-N), chemical oxygen demand (COD), and total phosphorus (TP) reached 43.40%, 41.18%, and 50.97%, respectively. The removal rate of AVS in the sediment reached 37.03%. The high-throughput sequencing showed that the relative abundance of anaerobic microorganisms in the sediment was significantly reduced, and that nitrogen and sulfur removal microorganisms appeared (e.g., Thermomonas, Dechloromonas, Proteus hauser, Desulfomicrobium, and Thiobacillus). Phosphorus in the sediment was converted into Fe/Al-P and Ca-P. Therefore, in-situ CaO2 combined with biochar coverage had a good repairing effect on black odorous sediment.

Performance of enhanced biological phosphorus removal and population dynamics of phosphorus accumulating organisms in sludge-shifting sequencing batch reactors.

The sludge-shifting sequencing batch reactor (SBR) is an enhanced biological phosphorus removal (EBPR) process for wastewater treatment. In this study, the enrichment of phosphorus accumulating organisms (PAOs) will be attempted by using different high concentration of substrates. In sludge-shifting SBR, activated sludge can be continuously shifted from the bottom of SBR to anaerobic zone/selector, which contains high concentration of substrates, through an orderly reflux between the paralleled SBRs. Denaturing gradient gel electrophoresis (DGGE) methods were used to monitor microbial diversity in sludge. Fluorescence in situ hybridization (FISH) was used to determine the microbial population profile and distribution map under different sludge shifting volumes. The synthesis of intracellular polymers in this process was also analyzed. Phosphorus removal efficiency as high as 96% ± 1.3% was achieved under a sludge shifting ratio of 30%. Synthetic efficiencies of polyhydroxybutyrate (PHB) by PAOs were improved at high sludge shifting ratios. FISH results demonstrated that the population of PAOs in the process increased under properly sludge shifting ratio and it significantly improved phosphorus removal efficiency. Sequencing results indicated that determined sequences (11 OTUs) belonged to Proteobacterium, Actinobacteria and Firmicutes, Pseudomonas kuykendallii, which played an important role in the process of P removal.

Performance and microbial community in a combined VF-HF system for the advanced treatment of secondary effluent.

In this study, a laboratory-scale system combined a vertical flow constructed wetland (VF) with a horizontal flow constructed wetland (HF), which was used to treat the secondary effluent of a wastewater treatment plant. Removal efficiencies of 67.02%, 89.80%, 90.31% and 75.38% were achieved by the system for chemical oxygen demand (COD), ammonium nitrogen (NH4 +-N), total nitrogen (TN) and total phosphorus (TP), respectively. The VF showed much higher average loading rates of COD, TP, NH4 +-N and TN (7.96 g/m2/d, 0.076 g/m2/d, 0.31 g/m2/d and 0.99 g/m2/d) than in HF (0.65 g/m2/d, 0.016 g/m2/d, 0.25 g/m2/d and 0.50 g/m2/d), during the stable operation period. Biodegradation played a major role in pollutant removal, especially for COD and TN. The results of bacterial community analysis indicated that heterotrophic denitrifying bacteria (Hydrogenophaga and Flavobacterium) were the dominant contributors for nitrogen removal in the VF, while heterotrophic denitrifying bacteria (Rhodobacter, Flavobacterium and Dechloromonas) and the autotrophic denitrifying bacteria Sulfurimonas played the principal roles for nitrogen removal in the HF. Redundancy analyses showed that COD and NH4 +-N were the important factors affecting the distribution of nitrogen removal bacteria in the VF, while pH, dissolved oxygen and oxidation-reduction potential were the key factors influencing the distribution of nitrogen removal bacteria in the HF.

[Treatment of Urban Runoff Pollutants by a Multilayer Biofiltration System].

In order to control the non-point source pollution from road runoff in Wuxi City effectively, a multilayer biofiltration system was designed to remove a variety of pollutants according to the characteristics of road runoff in Wuxi, and the experimental research was carried out to study the effect on rainwater pollution purification. The results show that the system has a good performance on removing suspended solids (SS), organic pollutant (COD), nitrogen and phosphorus: all types of multilayer biofiltration systems have a high removal rate for SS, which can reach 90%. The system with activated carbon (GAC) has higher removal rates for COD and phosphorus. The system with zeolite (ZFM) has a relatively better removal efficiency for nitrogen. The addition of wood chips in the system can significantly improve the system efficiency for nitrogen removal. Between the two configurations of layered and distributed wood chips, configurations of distributed wood chips reach higher COD, phosphorus and nitrogen pollutants removal efficiencies since they can reduce the release of wood chips dissolution.

[Urban non-point source pollution control by runoff retention and filtration pilot system].

A runoff retention and filtration pilot system was designed and the long-term purification effect of the runoff was monitored. Runoff pollution characters in 2 typical events and treatment effect of the pilot system were analyzed. The results showed that the runoff was severely polluted. Event mean concentrations (EMCs) of SS, COD, TN and TP in the runoff were 361, 135, 7.88 and 0.62 mg/L respectively. The runoff formed by long rain presented an obvious first flush effect. The first 25% flow contributed more than 50% of the total pollutants loading of SS, TP, DTP and PO4(3-). The pilot system could reduce 100% of the non-point source pollution if the volume of the runoff was less than the retention tank. Otherwise the overflow will be purification by the filtration pilot system and the removal rates of SS, COD, TN, TP, DTP and PO4(3-) reached 97.4% , 61.8%, 22.6%, 85.1%, 72.1%, and 85.2% respectively. The system was stable and the removal rate of SS, COD, TN, and TP were 98.6%, 65.4%, 55.1% and 92.6%. The whole system could effectively remove the non-point source pollution caused by runoff.