Abstract
In order to avoid eutrophication phenomena of surface water-courses, the reduction of the nutrient content, such as nitrogen and phosphorus, becomes ever more pressing. Respect to traditional depuration systems, the phytodepuration by microalgae presents different advantages: the simultaneous reduction of nitrogen and phosphorus by photosynthesis with biomass production without external organic sources and the production of oxygenated effluents after microalgae treatment. Moreover, the produced biomass could be used as raw material for energy or chemical purposes and the depuration systems with microalgae require less surface area than traditional phytodepuration ones. In this work data recovered from phytodepuration of rural municipal waste by microalgae are presented. Microalgae were grown in a semi-pilot photobioreactor system with a total capacity of 0.95 m3, consisting of: a photobioreactor composed by 40 vertical plexiglass tubes fed in parallel, a recycling vessel with a volume of 500 L, a recycling centrifugal pump and a submerged centrifugal feed pump. The area occupied by the plant was 5.4 m2. The photobioreactor was continuously fed with the final effluent of San Pietro Vara (Imperia, Italy) wastewater treatment plant and the effluent from the photobioreactor was piped in the no-longer used sludge draining bed, and from here in the feed sump. The microalgae growth has been identified by microscopic analysis. The predominant algal species were Chlorophyceae and Cyanophyceae, but the total biomass included also protozoa and small metazoan. Biomass concentration was recorded periodically. Two multiparamentric probes were used for the determination of pH, OD, NO3, NH4+, Chlorophyll-a, temperature and turbidity, while COD, total N and P were measured traditionally. The main results obtained from the closed system have been average removal of 50, 60 and 50 % for COD, total N and total P respectively. Results indicated that, in general, the outlet of phytodepuration met the quality standards required by law (Annex 5 – Italian Law 152/06 according to the EC Dir. 91/271).
