Nutrients Removal and Recovery in a Two-Stage High-Rate Algal Wastewater Treatment System

Abstract

Removal of wastewater borne nutrients by high rate algal ponds for the control of eutrophication in receiving bodies of water was studied under laboratory and outdoor conditions. Due to limitations of areal productivity and stoichiometry of nitrogen/algal bio-mass and phosphorus/algal biomass only less than 40 percent removal of nitrogen and phosphorus from strong municipal wastewater can be expected through biomass incorporation in one-stage high-rate algae ponds. Nitrogen removal of 74 percent can be attained by supplementary removal through ammonia atmospheric evolution from pond surface while phosphorus removal of 95 percent is attained following algae flocculation with alum. A second-stage pond following a “coarse” algae separation is needed to exert the full incorporation of nutrients into algal biomass. Effluent from the second stage, following “refined” algae separation, contain less than 4 mg/ℓ and less than 0.5 mg/ℓ of nitrogen and phosphorus, respectively. The final second stage effluent sustained reduced further algae productivity even when resupplemented by N and P and only addition of other macro and micro nutrients triggered additional significant algae growth, indicating depletion of algae growth potential factors other than N and P by the preceding two stages. The possibility of recovering the removed nutrient in the form of biomass proteinaceous animal feed is also discussed.

Microalgae wastewater treatment: Biological and technological approaches

“…The addition of N or P is sometimes used to ensure molar ratios of nutrients for optimal algal growth [75,76], and co-cultivation with bacteria can be favourable in relation to heterotrophic oxidation of organic compounds in wastewater by microorganisms that benefit from increased oxygen levels, induced by photoautotrophic algal growth [77][78][79]. The removal efficiency of total N and P by microalgae from wastewater has been determined to be between 10 and 97% and is highly dependent on culture mode, tank size, type of wastewater, and the microalgae strain [72,[80][81][82][83], indicating that there is no single technology/species combination that is able to fulfil every WWT goal. Alternative PBR technologies, such as tubular or flat-panel PBR systems, are designed to improve light distribution by minimizing the thickness of the surface layer and therefore providing a more efficient light penetration even in highly concentrated suspensions [84].…”

Elimination de l'azote et du phosphore dans un lagunage à haut rendement

“…La présence d'une agitation ou turbulence favorise le transfert de l'ammoniac de ta solution aqueuse vers l'atmosphère. Dans le LHR les conditions permettant la volatilisation de NH 3 sont réunies : l'activité algale intense qui s'y développe s'accompagne d'une augmentation du pH suite à l'assimilation photosynthétique des bicarbonates (AZOV, 1982 ;BUHR et MILLER, 1983 ;RICHMOND, 1986, DUBINSKY, 1986. Les pH peuvent atteindre des valeurs proches de 10.…”

Performance of a Single-Cell Aerated Waste Stabilisation Pond Treating Domestic Wastewater: A Three-Year Study

“…As in the case of NH 4 -N, alternation of periods with a net SRP removal and periods with a net SRP release led to a globally low SRP retention rate over the three studied years (Table 5). In the pond, SRP removal from the open water results either from the formation of Ca, Mn or Fe precipitates (GOLTERMAN, 1988;MOUTIN et al, 1992) or from the assimilation by algae or bacteria (SHELEF et al, 1982, VAN LOOSDRECHT et al, 1997. The sedimentation of these precipitates and organisms lead to significant SRP removal rates in some treatment plants such as non-aerated WSP and High Rate Algal Ponds where fixed SRP, in the presence of high Ca concentration (>10 mg l -1 ) and high pH (>8) (VOLLENWEIDER, 1976;GOLTERMAN, 1988), is not resolubilized (PICOT et al, 1991).…”