Photo-activated sludge: a novel algal-bacterial biotreatment for nitrogen removal from wastewater; Dissertation, Wageningen University and IHE Delft Institute for Water Education

Nitrogen rich wastewaters (10-400 mg N L-1) are usually produced by municipal, industrial and agricultural wastes, such as effluents from anaerobic treatments. These represent a risk to the environment due to the high nutrient concentrations (nitrogen and phosphorous), which can cause eutrophication of water bodies, deteriorating the quality of the ecosystems. As a solution, the potential nitrogen removal capacity of a novel bio-treatment system, namely the Photo-Activated Sludge (PAS), composed of microalgae and bacteria consortia, was studied. The aim of this research is to maximize the efficiency of microalgal-bacterial consortia for nitrogen removal. The research will focus on investigating the kinetics of the microorganisms involved (heterotrophs, autotrophs and phototrophs), and the optimal operational conditions such as hydraulic retention time (HRT) and solids retention time (SRT) in order to optimize the removal efficiency of the microalgal-bacterial consortia. Experimental work using photobioreactors for the cultivation of microalgae and bacteria under sequencing batch conditions showed that microalgal-bacterial consortia can remove ammonium 50% faster than solely microalgal consortia. The increase in ammonium removal rates was due to the action of nitrifying bacteria, supplied with oxygen produced by algae. Based on this, microalgal-bacterial consortia are able to effectively remove nitrogen at shorter SRTs and HRTs than usually used in algal systems, showing high ammonium removal efficiencies. Furthermore, this thesis propose design criteria for high rate algae ponds using the PAS system for wastewater treatment as a simple, yet innovative, technology with low energy requirements and high removal efficiencies of organic compounds and nutrients