Study On The Bioremediation Potential Of Porphyra Yezoensis

Today, in the field of marine ecology, the use of macroalgae bioremediation ofeutrophic waters is a hot research program. Choose macroalgae bioremediation shouldcomply with the following standards: First of all, the macroalgae selected must havehigh specific growth rate which is affected by a variety of environmental factors.Therefore, the study of the effects of specific growth rate under optimal environmentalfactors is an effective way to choose the appropriate macroalgae. Secondly, the growthin different periods can absorb large amounts of nutrients. Marine EnvironmentalQuality Bulletin2013released by China’s State Oceanic Administration show thatChina’s offshore top two major pollutants are inorganic nitrogen and active phosphate.Therefore, one of the most important criteria for selection of macroalgae is to look attheir uptake and removal efficiency of nitrogen and phosphorus, and thus achieve thepurpose of repairing eutrophic waters. Again, the absorption of nutrients by macroalgaecan synthesize their own organic ingredients. Macroalgae absorption N, P, and othernutrients to synthesize into tissue N, photosynthesis pigments and other physiologicalfunctions maintaining nutrients. Macroalgae through photosynthesis absorb largeamount of CO2, and transformed into organic matter. Finally, the selected macroalgaehave high economic value. Although selected macroalgae have higher growth rates andexcellent nutrient removal efficiency, but if it is not recovered back from the sea, it willdecay, and eventually reback into the ocean and made eutrophication. Therefore,environment factors and N、P concentration on the growth and nutrient removal capacitywere assessed in the laboratory to study the bioremediation potential of large-scale P.yezoensis cultivation.Porphyra yezoensis is an economic marine macroalgae cultivated widely along thecoast of the Yellow Sea, China. In this study, the effects of algal density (0.1,0.2,0.4,0.8, and1.6g·L-1), irradiance (30,60,90, and120μmol·m-2·s-1), temperature (5,10,15,20and25°C), photoperiod (8:16-h,12:12-h, and16:8-h light:dark [L:D]), salinity (10,15,20,25,30, and35), desiccation time (0,1,2, and4h), and N, P concentration on thegrowth and nutrient removal capacity were assessed in the laboratory to study thebioremediation potential of large-scale P. yezoensis cultivation. Each experiment wasconducted for2weeks. About3-week-old algae of length3–5cm were used. P.yezoensis thalli were grown in gently aerated250-mL bottles. Von Stosch enrichment (VSE) solution was added to the culture medium containing approximately500μmol·L-1NO3--N and30μmol·L-1PO43--P. The culture medium was renewed twice aweek; biomass was recorded as the fresh weight and the NO3--N and PO43--P contents inthe culture medium were measured. The results indicated that the growth rate ofPorphyra showed a negative correlation with algal density and a positive correlationwith irradiance. In2weeks, the maximal algal growth rate of38.1%·d-1was observed,with algal density of0.1g·L-1at an irradiance of120μmol·m-2·s-1. The minimal algalgrowth rate of12.6%·d-1was observed, with an algal density of1.6g·L-1at anirradiance of30μmol·m-2·s-1. The removal rates of NO3--N and PO43--P increased withincreasing algal density ranging from0.1g/L to0.8g·L-1, whereas no significantdifferences were noted when the algal density ranged from0.8g·L-1to1.6g·L-1. At analgal density of1.6g·L-1and irradiance of90μmol·m-2·s-1, the maximum NO3--N andPO43--P removal rates were97.3%(1.74mg N/d) and93.7%(0.21mg P/d), respectively.The following conditions were optimal for the growth and nutrition removal:temperature of15°C, photoperiod of16:8-h L:D, and salinity of25. At the aboveoptimal conditions, the maximum growth rate of36.9%was noted, with the highestNO3--N and PO43--P removal efficiencies. However, at25°C and photoperiod of8:16-hL:D, the minimum growth rate of7.5%·d-1was noted, with the lowest NO3--N andPO43--P removal efficiency. P. yezoensis could grow in a wide salinity range, from10to35. The maximal growth rate of37.9%·d-1, with the maximum NO3--N and PO43--Premoval rates of96.5%(1.70mg N/d) and86.9%(0.20mg P/d), respectively, wereobserved under25salinity and no desiccation (0h). Although desiccation treatment hada negative effect on the growth and nutrition removal rate, it strengthened thephysiological activity. The growth rate and nutrient removal efficiency ofno-desiccation groups were higher than those in desiccation groups. Further, lowsalinity and long desiccation time greatly inhibited algal growth and nutrient uptake;however, the photosynthesis rate in desiccation groups was higher than that inno-desiccation groups.Effect of nutrients on the specific growth rate of P. yezoensis showed that it cantolerant high concentration of NH4+-N. P. yezoensis all can grow normally by NH4+-Nconcentration from0to600μmol·L-1. The maximum specific growth rate is31.9%·d-1when the NH4+-N concentration is300μmol·L-1. PO43--P concentration from10μmol/Lto40μmol·L-1the algae have high specific growth rate, while when the PO43--Pconcentration below10μmol·L-1or exceed40μmol·L-1, the specific growth rate is low.Specific growth rate increased with N/P increased, optimal growth rate in the N/P ratiowas10-20. Effect of environment factors and N, P concentration on the tissue C, tissue N, C/N,pH of the culture medium and pigment content showed thatpH of the algae culture medium was increased with the increase of culture time andalgae density increased. With Irridiance90μmol·m-2·s-1, algae density1.6g·L-1, the pHof the culture medium up from the initial8.0to9.5after3days experiment.Phycobiliproteins and chlorophyll content decreased with the increase of algae densityincreased with the increase of ammonia concentration, and the highest Phycobiliproteincontent is34.6mg/g. Tissue N of P. yezoensis is from3.16%to7.68%which wasincreased with the increase of N concentration. The C/N ratio is from5.19to12.55.Overall, P. yezoensis showed rapid growth rate, high commercial value, andefficient nutrient concentration, making it an excellent candidate for bioremediation.The study results may be useful for applying P. yezoensis for remediation in coastalwaters worldwide.