Chunxia Ma

The removal of cyanobacteria and their metabolites through anoxic biodegradation in drinking water sludge

The effects of environmental factors on cyanobacteria damage and microcystin-LR degradation in drinking water sludge were investigated under anoxic conditions. The rates of microcystin-LR release and degradation increased rapidly with the increasing temperature from 15°C to 40°C and the highest degradation rate of 99% was observed at 35°C within 10days. Compared to acidic conditions, microcystin-LR degraded more rapidly in weak alkali environments. In addition, the microbial community structures under different anoxic conditions were studied. The sequencing results showed that four phyla obtained from the DGGE profiles were as follows: Proteobacteria, Acidobacteria, Firmicutes and Cyanobacteria. Proteobacteria containing nine genera were the most common species. Pseudomonas, Methylosinus and Sphingomona all showed stronger activities and had significant increase as microcystin-LR degraded, so they should be responsible for the microcystin-LR degradation. This is the first report of Pseudomonas, Methylosinus and Sphingomonas as the microcystins-degrading microorganisms in anoxic drinking water sludge.

A promising application of chitosan quaternary ammonium salt to removal of Microcystis aeruginosa cells from drinking water

This work was aimed toward studying the new application of chitosan quaternary ammonium salt (HTCC), a water-soluble chitosan derivative, on removal of Microcystis aeruginosa (M. aeruginosa) cells during HTCC coagulation and floc storage. Results showed that all cells were removed without damage under optimum coagulation conditions: HTCC dosage 1.5mg/L, rapid mixing for 0.5min at 5.04g and slow mixing for 30min at 0.20g. The high removal efficiency was due to the large size and compact structure of flocs formed by HTCC, which readily settled. During floc storage, HTCC could induce production of reactive oxygen species (ROS), which would accelerate M. aeruginosa cell lysis. But the flocs, into which the cells aggregated, could protect cells from cellular oxidative damage caused by ROS, thus keeping the cells intact for a longer time.

Behaviors of Microcystis aeruginosa cells during floc storage in drinking water treatment process.

This is the first study to systematically investigate the different behaviors of Microcystis aeruginosa in the sludges formed by AlCl3, FeCl3, and polymeric aluminium ferric chloride (PAFC) coagulants during storage. Results show that the viability of Microcystis aeruginosa in PAFC sludge was stronger than that of cells in either AlCl3 or FeCl3 sludge after the same storage time, while the cells’ viability in the latter two systems stayed at almost the same level. In AlCl3 and FeCl3 sludges high concentrations of Al and Fe were toxic to Microcystis aeruginosa, whereas in PAFC sludge low levels of Al showed little toxic effect on Microcystis aeruginosa growth and moderate amounts of Fe were beneficial to growth. The lysis of Microcystis aeruginosa in AlCl3 sludge was more serious than that in PAFC sludge, for the same storage time. Although the cell viability in FeCl3 sludge was low (similar to AlCl3 sludge), the Microcystis aeruginosa cells remained basically intact after 10 d storage (similar to PAFC sludge). The maintenance of cellular integrity in FeCl3 sludge might be due to the large floc size and high density, which had a protective effect for Microcystis aeruginosa.

Significantly enhanced dewatering performance of drinking water sludge from a coagulation process using a novel chitosan–aluminum chloride composite coagulant in the treatment of cyanobacteria-laden source water

The enhanced dewatering performance and the fate of cyanobacterial cells in the filtration of cyanobacteria-laden sludge, generated by a coagulation process using a novel composite chitosan–aluminum chloride (CTSAC) coagulant, were systemically studied. Two other cyanobacteria-laden sludge, aluminum chloride (AC) sludge and chitosan (CTS) sludge, were also studied to compare dewater performance with CTSAC sludge. Results showed that the dewatering process did not cause cell lysis and microcystins (MCs) release. The level of MCs and extracellular organic matter (EOM) in the filtrate were decreased by adsorption and sieving onto the cake layer formed on the membrane, but dewatering at high vacuum pressure reduced the rejection efficiency. The sludge from the coagulation process using the CTSAC composite displayed better sludge dewaterability and obtained a better quality of filtrate (fewer MCs and EOM) than those from AC and CTS coagulation processes independently. A three-dimensional excitation–emission matrix (EEM) fluorescence measurement indicated that protein-like substances in soluble extracellular polymeric substances (EPS) played a negative role on cyanobacteria-laden sludge dewatering. In addition, CTSAC sludge showed a more compact structure and larger floc sizes than AC sludge and CTS sludge for a strong improvement in the charge neutralization and bridge ability of AC by combining CTS in the composite coagulant. It was further observed that floc size played a more significant role on sludge dewaterability than the degree of compactness. Overall, the preferable dewater performance of CTSAC sludge demonstrated the CTSAC composite coagulant has great potential for the treatment of cyanobacteria-laden source water.

The enhanced reduction of C- and N-DBP formation in treatment of source water containing Microcystis aeruginosa using a novel CTSAC composite coagulant

This study investigated the effect of a chitosan-aluminium chloride (CTSAC) composite coagulation process on reducing the formation of algal organic matters (AOM) related carbonaceous disinfection by-products (C-DBPs) and nitrogenous disinfection by-products (N-DBPs), by removing or adsorbing their precursors. Compared with aluminium chloride (AC) and chitosan (CTS) alone, CTSAC significantly enhanced the removal of dissolved organic matter (DOC), polysaccharide, protein and humic acids, attaining removals of 64.95%, 80.78%, 70.85% and 44.50%, respectively. Notably, the three-dimensional excitation and emission matrix (3D-EEM) combined with molecular weight (MW) fractionation analysis revealed that CTSAC was not only effective for removing high-MW AOM, but also for the low-MW fractions that are important in forming DBPs. In addition, the CTSAC coagulation was proven to enhance the removal of aromatic polypeptide/amino acid-like materials and aliphatic amines, which have high N-nitrosodimethylamine formation potential. Efficient AOM removal by the CTSAC coagulation resulted in significant reduction of both AOM-related C-DBPs (63.54%) and N-DBPs (71%), while AC coagulation did not substantially reduce the formation of tribromomethane, 1,1,1-trichloropropanone or N-nitrosodimethylamine, and CTS coagulation alone did not achieve any obvious reduction in trichloronitromethane. Fourier transform infrared (FT-IR) spectroscopy analysis confirmed the interaction of CTS and AC in the CTSAC composite coagulation, which contributed to the improved AOM removal performance of CTSAC, and, in this case, reduced the formation of C- and N-DBPs.

16S rRNA Gene Amplicon Sequencing Reveals Significant Changes in Microbial Compositions during Cyanobacteria-Laden Drinking Water Sludge Storage

This is the first study to systematically investigate the microbial community structure in cyanobacteria-laden drinking water sludge generated by different types of coagulants (including AlCl3, FeCl3, and polymeric aluminum ferric chloride (PAFC)) using Illumina 16S rRNA gene MiSeq sequencing. Results show that Cyanobacteria, Proteobacteria, Firmicutes, Bacteroidetes, Verrucomicrobia, and Planctomycetes were the most dominant phyla in sludge, and because of the toxicity of high Al and Fe level in AlCl3 and FeCl3 sludges, respectively, the PAFC sludge exhibited greater microbial richness than that in AlCl3 and FeCl3 sludges. Due to lack of light and oxygen in sludge, relative abundance of the dominant genera Microcystis, Rhodobacter, Phenylobacterium, and Hydrogenophaga clearly decreased, especially after 4 days storage, and the amounts of extracellular microcystin and organic matter rose. As a result, the relative abundance of microcystin and organic degradation bacteria increased significantly, including pathogens such as Bacillus cereus, in particular after 4 days storage. Hence, sludge should be disposed of within 4 days to prevent massive growth of pathogens. In addition, because the increase of extracellular microcystins, organic matter, and pathogens in AlCl3 sludge was higher than that in FeCl3 and PAFC sludges, FeCl3 and PAFC may be ideal coagulants in drinking water treatment plants.

The lysis and regrowth of toxic cyanobacteria during storage of achitosan–aluminium chloride composite coagulated sludge: implications for drinking water sludge treatment

Coagulation is a key unit operation for cyanobacterial cell removal; however, the potential danger of cyanobacterial cells transferred into sludge is not well understood. In this study, the fate of Microcystis aeruginosa (M. aeruginosa) and secondary metabolites in chitosan–aluminium chloride (CTSAC) coagulated cyanobacteria-laden sludge were investigated during the sludge storage period. The extracellular microcystins (MCs) can be adsorbed onto the CTSAC flocs for six days with a reduced biodegradation rate. Less M. aeruginosa cell lysis was observed in the coagulated system than in the natural cell system, due to the protection of M. aeruginosa by the CTSAC. Furthermore, the residual Al content decreased in the cyanobacteria-laden sludge supernatant. The amount of extracellular organic matter (EOM) stayed low in the coagulated system for four days. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis showed that coexisting bacteria reduced in the sludge during the initial four days storage time. Interestingly, the CTSAC degradation favored the growth of the M. aeruginosa cells. This study will be helpful for better understanding and managing secondary metabolite pollution problems related to coagulation-generated cyanobacteria-laden sludge during the sludge supernatant recycling process. The use of CTSAC composite coagulant is of practical value in reducing secondary pollution during cyanobacteria-laden sludge storage.

Inactivation of Microcystis aeruginosa by hydrogen-terminated porous Si wafer: Performance and mechanisms

We proposed a method to inactivate Microcystis aeruginosa by using hydrogen-terminated porous Si (H-PSi) wafer. The influences of oxidation time on the removal of M. aeruginosa were investigated. Samples oxidized by H-PSi wafer were subsequently grown under illuminated culture conditions. The results demonstrated that the optimal oxidation time was about 1h, which could control the growth of M. aeruginosa about 65%, after 3days culture. Simultaneously, extracellular microcystins was decreased from 14.65 to 7.06μgL(-1) and remain relative integrity of M. aeruginosa cells which could avoid secretion of large amounts of organic material. Multiple analysis techniques including fluorescence excitation-emission matrix (EEM) and fluorescence microscope were used to reveal the inhibition mechanisms of M. aeruginosa. Meanwhile, analyses of reactive oxygen level, malondialdehyde content, and superoxide dismutase activity indicated that the damage and inactivate of M. aeruginosa cells are mainly due to accumulation of lipid peroxidation and inhibition of normal physiological metabolism by free radicals produced by H-PSi wafer under visible light irradiation. In conclusion, these results suggest that H-PSi wafer may be useful in controlling growth and survival of M. aeruginosa in many large lakes and reservoirs, thus mitigating many of the economic, esthetic ecological impacts of the invasive alga.

Effects of glucose on microcystin-LR removal and the bacterial community composition through anoxic biodegradation in drinking water sludge

To enhance the degradation efficiency of microcystin (MC) in drinking water sludge (DWS), the underlying mechanisms between organic carbon (glucose) and the biodegradation of MC-LR under anoxic conditions were investigated by polymerase chain reaction-denaturing gradient gel electrophoresis technology. The addition of glucose reduced the rate of the MC-LR biodegradation indicating the occurrence of inhibition of degradation, and an increased inhibition was observed with increases in glucose concentration (0–10,000 mg/L). In addition, the community analysis indicated that the variety and the number of the microbes increased with the concentration of glucose amended (0 –1000 mg/L), but they decreased substantially with the addition of 10,000 mg/L of glucose. The phyla Firmicutes, Proteobacteria and Chloroflexi were found to be the dominant. Methylobacterium and Sphingomonas were MC-degrading bacteria and used glucose as a prior carbon source instead of MC, resulting in the decrease in the MC-LR biodegradation rate under anoxic conditions. Thus, reducing organic carbon could improve the anoxic biodegradation efficiency of MC in DWS.

Using quartz sand to enhance the removal efficiency of M. aeruginosa by inorganic coagulant and achieve satisfactory settling efficiency

In this study, low-cost and non-polluting quartz sand was respectively mixed with AlCl3, FeCl3 and PAFC to synergistically remove Microcystis aeruginosa. Results showed that quartz sand could markedly increase the algae removal efficiency and decrease the coagulant doses. The increase of removal efficiency with AlCl3 and FeCl3 was only due to the enhancement of floc density by the quartz sand. However, the removal efficiency with PAFC was increased not only by the enhanced floc density, but also by the enlarged floc size. Flocs from 50 mg/L sand addition were larger than that with other sand doses, which was on account of the appropriate enhancement of collision efficiency at this dose. After coagulation, the extracellular organic matter (EOM) and microcystins (MCs) in system with quartz sand was remarkably reduced. That’s because quartz sand can enhance the coagulation so as to improve capping the EOM and MCs in flocs during coagulation process. Owing to 200 mg/L quartz sand could damage the cell’s membrane during coagulation proces, algal cells in the system lysed two days earlier than with 50 mg/L sand during flocs storage. In addition, cells with PAFC incurred relatively moderate cellular oxidative damage and could remain intact for longer time.