Bioresource Technology, Volume 169, 2014, Pages 27-32.
Francesco G. Gentili.
Department of Wildlife, Fish and Environmental Studies, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
The aim of the study was to grow microalgae on mixed municipal and industrial wastewater to simultaneously treat the wastewater and produce biomass and lipids. All algal strains grew in all wastewater mixtures; however, Selenastrum minutum had the highest biomass and lipids yields, up to 37% of the dry matter. Nitrogen and phosphorus removal were high and followed a similar trend in all three strains. Ammonium was reduced from 96% to 99%; this reduction was due to algal growth and not to stripping to the atmosphere, as confirmed by the amount of nitrogen in the dry algal biomass. Phosphate was reduced from 91% to 99%. In all strains used the lipid content was negatively correlated to the nitrogen concentration in the algal biomass. Mixtures of pulp and paper wastewater with municipal and dairy wastewater have great potential to grow algae for biomass and lipid production together with effective wastewater treatment.
Nowadays, the world population is facing a major problem that is to satisfy the constantly increasing energy demands in an environmentally friendly way. However, this is a particularly difficult and challenging task both from an economical and an environmental point of view. Furthermore from the seventies to the first decade of the 21st century fossil fuels are still the predominant source of energy.
Production of algae using nutrients from wastewater and CO2 from flue gases will not only result in CO2-fixation, but also in the production of biomass with a harvesting time that is very fast (12-36). The possibility of using marginal land and a continuous automated system with very high flow-through capacities makes the algae system particularly interesting. The reclamation of wastewater, both municipal and industrial, is of pivotal importance to achieving sustainability in our society at the global level. Often in traditional and well established wastewater treatment techniques the reduction of nitrogen and phosphorus is energy demanding. On the one hand, traditional treatments efficiently reduce the concentration of N and P; on the other hand, the treatments waste these important and vital nutrients through denitrification or deposition in landfill.
Phosphorus resources are limited and we are rapidly approaching production peak; hence, recycling this vital element is a pivotal challenge of the 21st century.
The pulp and paper industry is the world’s largest producer of plant-based wastewater. Consequently, the pulp and paper industries produce a great amount of wastewater that has to be treated before being released into the environment. Even though the wastewater from the pulp and paper industry is rich in carbon it is limited in nitrogen and phosphorus. Hence in conventional wastewater treatment processes in the pulp and paper industry nutrients addition has been carried out to ensure microorganisms growth for treating the wastewater. However to overcome nutrients limitation pulp and paper wastewater can be mixed with nutrients rich wastewater such as municipal and dairy. In such wastewater mixtures ammonium was reduced from 96% to 99%; phosphate was reduced from 91% to 99%; one algal strain had lipids yields, up to 37% of the dry matter.
Mixtures of pulp and paper wastewater with municipal and dairy wastewater have great potential to grow algae for biomass and lipid production together with effective wastewater treatment.