Sanjay B. Pawar

Microalgal bioremediation of food-processing industrial wastewater under mixotrophic conditions: Kinetics and scale-up approach

AbstractThe Chlorella microalgae were mixotrophically cultivated in an unsterilized and unfiltered raw food-processing industrial wastewater. Both inorganic carbon (CO2-air) and organic carbon (wastewater) were provided simultaneously for microalgae growth. The aim of the study is to find out the utilization rates of total organic carbon (TOC) and chemical oxygen demand (COD) under mixotrophic conditions for a given waste water. About 90% reduction in TOC and COD were obtained for all dilutions of wastewater. Over 60% of nitrate and 40% of phosphate were consumed by microalgae from concentrated raw wastewater. This study shows that microalgae can use both organic and inorganic sources of carbon in more or less quantity under mixotrophic conditions. The growth of microalgae in food-processing industrial wastewater with all studied dilution factors, viz. zero (raw), 1.6 (dilution A), and 5 (dilution B) suggests that the freshwater requirement could be reduced substantially (20%–60%). The degradation kinetics also suggests that the microalgae cultivation on a high COD wastewater is feasible and scalable.

Bioremediation of synthetic high–chemical oxygen demand wastewater using microalgal species Chlorella pyrenoidosa

ABSTRACT The microalgal species Chlorella pyrenoidosa was cultivated in synthetic wastewater of initial chemical oxygen demand (COD), nitrate, and phosphate concentrations of 5000, 100, and 40 mg/L, respectively. The aim of the study was to find out the tolerance of microalgae to different COD concentrations and the extent of COD degradation at those concentrations. Three dilutions of wastewater (initial COD concentrations 5000, 3000, and 1000 mg/L) and three inoculum sizes (0.1, 0.2, and 0.3 g/L) were considered for the study. The experimental parameters such as total organic carbon, total inorganic carbon, COD, optical density, total solids, nitrate, and phosphate were measured on a daily basis. Biodegradation kinetics was determined for all cases using first-order reaction and Monod degradation equations. Optimal results showed that up to 90% reduction in TOC was obtained for 1000 COD wastewater while only 38% reduction in total organic carbon (TOC) was achieved for 5000 COD wastewater. Over 95% reduction in nitrate and nearly 90% removal of phosphate were obtained with the lowest microalgal inoculum concentration (i.e., 0.1 g/L) for all COD dilutions. This study showed that microalgal species C. pyrenoidosa can successfully degrade the organic carbon source (i.e., acetate) with significant removal efficiencies for nitrate and phosphate.

An integrated approach for microalgae cultivation using raw and anaerobic digested wastewaters from food processing industry

An integrated approach has been proposed to produce microalgal biodiesel using both raw wastewater (RW) and anaerobically digested wastewater (ADW) of food processing industry without addition of extra nutrients or carbon source for cultivation besides obtaining effluent discharge permissible limits of TN, TP, and COD. Three microalgae species cultivated with following different combinations: RW, ADW, RW + ADW, and glucose + ADW. Results indicated that the addition of RW as a carbon source in ADW significantly enhanced BP, LP, and TN removal as compared to the ADW alone. The runs with RW + ADW removed COD, TN, and TP by 89%, 84%, and 70%, respectively. Sc. obliquus showed highest biomass and lipid productivities (211 and 27.5 mg L-1 d-1) for RW + ADW. The addition of RW or glucose in ADW significantly lowered PUFA contents to 5-15% CDW (as against 35-50% with ADW) for Chl. sorokiniana and Sc. obliquus.

Mass Production of Microalgae in Photobioreactors for Biodiesel Application: Selection, Limitations, and Optimization

The algal biodiesel is produced in four steps: cultivation, harvesting and dewatering, lipid extraction, and transesterification reaction (converting lipids to fatty acid methyl esters, FAME, i.e., biodiesel). Microalgae cultivation in photobioreactor (PBR) is not only costly but also very challenging step among the steps of algal biodiesel production. In this chapter, the advantages and disadvantages of various types of PBR have been discussed in the context of mass production at outdoor conditions. Several environmental limitations which affect the performance of PBR are critically reviewed with respect to the selections of PBRs and microalgae strains. The mode of cultivation was found to affect the biomass and lipid productivity under different conditions. Thus, an overview suggesting the optimal ways to enhance the total lipid content of microalgae under different modes of cultivation is discussed in this chapter. The research work of microalgae cultivation on wastewater is tabulated and discussed in the context of feasibility of process. The quality of biodiesel strongly depends on the proportion of saturated and unsaturated fatty acids. Thus, various process parameters and strategies which affect the lipid’s composition are also discussed in detail.