Screening of fresh water microalgae and Swedish pulp and paper mill waste waters with the focus on high algal biomass production
Examensarbete för masterexamen
Biotechnology (MPBIO), MSc
Microalgae as a source of feedstock for biofuels production recently have restored attention due to the current concerns regarding high oil prices and environmental impacts. Biomass derived from microalgae can positively contribute to the issue from two points of view: CO2 bio-fixation and concomitant reduction of nitrogen and phosphorus from waters would lead to environmental sustainability and the biomass yielded could be used to produce biofuel or other valuable products. Industrial waste waters are potential substitute of traditional media used for microalgae cultivation. For decades, algae have been used for treating waste water in different industries taking advantage of their high removal efficiency of nitrogen and phosphorus. However, using waste water for achieving a high algal biomass production is a different scenario. In this aspect, the focus is to get the highest possible cell mass when using the waste water, instead of just ensuring minimal levels of N and P in the treated water. Pulp and paper mills are major consumers of water resources and these industries discharge a huge amount of water to nearby lakes or rivers. The current research work investigated whether pulp and paper mill waste water is suitable for microalgae cultivation with the aim to achieve significant biomass production. Nine different process waters from five Swedish pulp and paper mills were tested with nine fresh water species of microalgae. Six of these waters were unable to support growth of microalgae due to color, turbidity and toxicity issues. Only three waters collected from Holmen Paper, Arctic Paper Munkedals AB, and Billerud Gruvön mill were able to support growth of the nine tested microalgae to a limited extent. During scale up, through a lab constructed gas distribution system, 1% CO2 was added to the cultures to enhance the algal growth (flow rate of 2000 ml/min. In these scaled-up cultivations, three fresh water microalgae were used: Chlamydomonas reinhardtii, Scenedesmus obliquus and Dictyosphaerium pulchellum. The highest cell concentration was achieved only when the waste waters were supplemented with nutrients (either with municipal water or with nitrate and phosphate salts), which indicated that one of the major limiting factors was low nutrient concentrations present in the waste waters. The order of growth for these three microalgae was similar (D. pulchellum> S. obliquus > C. reinhardtii), irrespective of type of water. There was no noticeable difference in growth, while growing in ammonium rich waste water and nitrate rich waste water. After two weeks of microalgae cultivation in Holmen Paper waste water supplied with nitrate and phosphate, the highest biomass was achieved by D. pulchellum (1.36 g/L). More than 90% of phosphate-P and around 65-81% nitrate-N was removed by the three fresh water microalgae. Thus, serious attention needs to be put on nutrient concentration levels while using pulp and paper mill waste water for microalgal biomass production.
Industriell bioteknik , Energi , Industrial Biotechnology , Energy