Antioxidant Response Of Microalgae Biofilm To Oxidative Stress And Effectiveness In Pollutant Removal

In this thesis,based on the existing work of the research group,combined with the local water pollution situation and pollution control requirement of Nigeria,the effectiveness of microalgae biofilm in aquatic pollutant removal,and the antioxidant response of microalgae biofilm to oxidative stress were investigated.The main contents of this thesis include:1)The function of microalgae biofilm cultured in nutrient-rich water as a tool for phycoremediation of petroleum polluted water;2)the role of microalgae biofilm native to petrochemical polluted stream in the remediation of water from River Kaduna;3)the efficiency and antioxidant response of microalgae biofilm in the phycoremediation of tannery,textile,and dyeing wastewater;4)the effect of nutrient and light illumination on oxidative stress of the microalgae biofilm,and on the antioxidant response of the biofilm to counteract the effect of ROS;and 5)the influences of Lemna minor L.,Chlorella vulgaris,and Aphanizomenon flos-aquae to freshwater microalgae biofilm formation and antioxidant responses to ROS production.To investigate the function of microalgae biofilm cultured in nutrient-rich water as a tool for phycoremediation of petroleum polluted water,microalgae biofilm cultured in nutrient-rich water was placed in a bioreactor with simulated petroleum-contaminated water,and left for eight weeks.The physicochemical parameters of the petroleum-contaminated water were determined before and after the treatment.Before and after treatment,the microalgae biofilm was also characterized.Some phytochemical constituents of the microalgae biofilm were also determined before and after the treatment.The results obtained show that microalgae biofilm cultured in the nutrient rich water is effective in improving the quality of the petroleum contaminated water(removal for the paremeters:turbidity(81.0%),conductivity(51.2%),sulphate(17.5%),alkalinity(28.4%),chloride(14.6%),total dissolve solid(TDS)(7.9%),total suspended solid(TSS)(26.0%),nitrate(33.0%),salinity(23.4%),Fe(16.0%),K(22.0%),(28.2%),Cr(13.6%),Mg(30.3%),Zn(40.5%),chemical oxygen demand(COD)(8.0%),biological oxygen demand(BOD)(16.7%)and total petroleum hydrocarbon(TPH)(15.0%)).The characterization of microalgae biofilm demonstrates the potential of microalgae biofilm to adsorb contaminants in petroleum-contaminated water,due to the existence of micropores and greater surface area of the microalgae forming the biofilm,or due to the presence of the extracellular polymeric substances(EPS)with high absorption efficiency.Analysis of the phytochemical parameters of the microalgae biofilm indicate the role of the chemical components in contaminants degradation,and the antioxidant response of the microalgae to counteract the oxidative impact induced by the microalgae’s exposure to contaminated water.To study the role of microalgae biofilm native to petrochemical polluted stream in the remediation of water from River Kaduna,microalgae biofilm was grown naturally in the bioreactor for seven months,in water collected from a stream receives effluent rich in organic and inorganic pollutants,without any nutrient addition.Then,the microalgae biofilm was used to treat water sampled from River Kaduna for one week.The reduction efficiency of some parameters/components was determined.The surface morphology of the microalgae biofilms was assessed before and after the treatment of River Kaduna water,using scanning electron microscope(SEM),X-ray fluorescence(XRF),X-ray diffractometer(XRD),and Fourier-transform infrared spectroscopy(FTIR).GC-MS was used to assess the phytochemical composition of the microalgae biofilm.The results also show the effectiveness of microalgae biofilm native to petrochemical polluted stream in the phycoremediation of water from River Kaduna.The reduction efficiency of some parameters/chemicals is high(turbidity(71.0%),conductivity(9.8%),sulfate(37.5%),alkalinity(62.5%),chloride(11.5%),TDS(9.9%),TSS(66.7%),nitrate(42.9%),COD(24.0%),BOD(33.0%),Cd(70.0%),Ni(74.0%)and Pb(71.0%)),indicating the effectiveness of the freshwater biofilm in the removal of pollutants.Other characterizations also buttressed that adsorption was the primary mechanism for the removal of pollutants from water by the freshwater microalgae.Microalgae biofilm was grown in a photo-bioreactor with BG 11 as the culture medium,to investigate the efficiency and antioxidant reaction of microalgae biofilm during the phycoremediation of tannery,textile,and dyeing wastewater.Beside some physicochemical parameters,some biochemical parametersarameters related to the antioxidant response of the microalgae biofilm,including peroxidase activity,catalase activity,superoxide dismutase activity(SOD),glutathione reductase,flavonoid,anthocyanin,carotenoid,phosphomolybdate scavenging activity,hydrogen peroxide scavenging activity,and DPPH scavenging activity,were determined before and after the treatment.The removal efficiencies of parameters/chemicals such as BOD,COD,TSS,oil,phenol,phosphate and total chromium were measured.Total organic carbon(TOC),and lipid content of the microalgae biofilm were also determined.The obtained findings illustrate the antioxidant response of microalgae biofilm during phycoremediation of tannery,textile,and dyeing wastewater.The findings indicate that microalgae biofilm is efficient at reducing BOD,COD,chlorides,TDS,TSS,sulfide,sulfate,oil and grease,phenol,phosphate,and total chromium from the wastewater.The findings also show an increase in peroxidase activity,catalase activity,SOD activity,and glutathione reductase activity,suggesting the role of enzymatic antioxidants in pollutant degradation and counteracting ROS impact.The decrease in flavonoid,anthocyanin,and carotenoid levels indicates the involvement of the non-enzymatic antioxidants in degradation and the role in osmoregulatory balance maintenance.Concurrently,the rise in TOC and lipid content suggests the essential role of antioxidants in radical scavenging.Increased phosphomolybdate capacity activity,hydrogen peroxide scavenging activity,and DPPH scavenging activity are both good indicators of high ROS output and protection of its effects.The capacity of the microalgae biofilm to expel contaminants from wastewater is due to the activities of enzyme release by the microalgae or adsorption of the pollutants to the wall of the biofilm participant microalgae.Microcystic aeruginosa and Aphanizomenon flos-aquae were used as model organisms to study the effect of nutrient and light illumination on oxidative stress of the microalgae biofilm,and on the antioxidant response of the biofilm.M.aeruginosa and A.flos-aquae were grown in an incubator under different illumination periods,to obtain corresponding microalgae biofilms.The concentration of ROS produced during the culturing period was monitored.The offsite measurement was performed to determine the enzymatic activities of the freshwater microalgae species’extract,including the measurement of SOD,catalase,and glutathione reductase activities.Non-enzymatic activities,including hydrogen peroxide scavenging activities,phosphomolybdate scavenging activities,reducing capacity,and DPPH scavenging activities,were also monitored.The effect of nutrients on biomass concentration,ROS content,chlorophyll content,lipid content,total enzymatic antioxidant reducing power,and total antioxidant activities was monitored.The effect of illumination on some antioxidant production,including anthocyanin,flavonoid,and carotenoids,which are useful for man,was also monitored.The results reveal that increased illumination promotes oxidative stress in M.aeruginosa and A.flos-aquae,resulting in high level of H2O2 and O2~-(H2O2 was 0.370 and0.590 mmol/L in M.aeruginosa and A.flos-aquae,respectively,and O2~-was 0.094 and 0.110mmol/L in M.aeruginosa and A.flos-aquae,respectively).The study also found that M.aeruginosa and A.flos-aquae have the potential to counteract the oxidative effects of ROS through enzymatic and non-enzymatic antioxidant mechanisms.According to the results,an increase in nutrient concentration raised the biomass of M.aeruginosa from 0.80 to 1.25 g/L and A.flos-aquae from 0.80 to 1.23 g/L.The increase in nutrient concentration also resulted in a high production of H2O2 and O2~-by the microalgae biofilm.With increased nutrient concentration,the mean level of H2O2 and O2~-produced by M.aeruginosa is 1.00 and 0.40mmol/L,respectively,while mean level of H2O2 and O2~-produced by A.flos-aquae is 0.40and 0.16 mmol/L,respectively.To study the influences of Lemna minor L.,Chlorella vulgaris,and Aphanizomenon flos-aquae on freshwater microalgae biofilm formation and antioxidant responses to ROS production,C.vulgaris and A.flos-aquae were grown in bioreactors containing water,BG 11growth medium,and the presence of L.minor L.The offsite measurements performed include ROS determination,chlorophyll,carotenoid,flavonoid,anthocyanin,SOD,peroxidase,catalase,glutathione reductase activities,antioxidant reducing power,phosphomolybdate activity,DPPH reduction activity,H2O2 scavenging activity,lipid content and organic carbon.The analysis of how L.minor L.,C.vulgaris,and A.flos-aquae affect microalgae biofilm formation and oxidative stress in the systems reveals that the involvement of C.vulgaris and A.flos-aquae resulted in the dominance of these microalgae in the biofilm,and the increase in ROS production.The research also discovered that the involvement of L.minor L.appeared to decrease the oxidative stress in the microalgae biofilm and resulted in low ROS production.The results of this thesis will help to further understand the mechanisms of the interaction between microalgae and pollutants,and the mechanism of producing ROS and biological antioxidation.They are helpful to understand the environmental behavior and ecological significance of natural biofilm in aquatic environment.They also provide supports for the establishment of pollution control and remediation systems based on natural microalgae biofilm.