SummaryA source of high-quality protein for animal feed. based upon algae recovered in the process of upgrading waste oxidation pond effluents and promising to be particularly economical. is being developed at the Technion. Unlike other types of single cell protein (SCP), the algal protein does not have to return the full production cost but only that of concentration and final processing. The balance is shared by the value of waste disposal and the reclaimed water. Whereas such systems as activated sludge require considerable mechanical energy to supply the oxygen needed for aerobically degrading organics in wastewater. oxidation ponds utilize solar energy for that purpose. The sludge obtained when their effluents are clarified consists largely of algae. bacteria, fungi. and zooplankton in relative proportions varying with operating conditions, and contains 40-60% (dry basis) high-quality protein. The highrate oxidation pond (a particularly intensive type of pond) produces on the average 34 g/m*/day solids, or over 100 tons/ha (hectare) annually. Two clarification routes have been found promising: centrifugation and alum flocculation followed by frothflotation. The latter route is less expensive in terms of both fixed and operating cost, and gives clarified effluent of higher quality. which can be seasonally stored with minimal eutrophication because the aluminum removes most of the phosphate from the effluent. A good product has been obtained by drum-drying the concentrate. and preliminary feeding tests have indicated that it can replace at least '4 of the soymeal in broiler rations and ?4 of the fishmeal in carp feed. N o ill effect of the aluminum in the product recovered by alum flocculation has been found so far, but a process for removing and recycling the aluminum has been developed nonetheless. in case ill effects do show up in further tests. The combined value of the benefits derived from a system centered around the high-rate oxidation pond with clarification by flocculation-flotation. in terms of waste treatment by alternative means. potable water saved. and soymeal replaced, significantly exceeds estimated cost.

Theoretical considerations confirmed by outdoor experiments indicated carbon limitation of biomass production in high-rate oxidation ponds at certain seasonal and operational conditions. Apparently, free carbon dioxide concentration in the pond is the major determinant of carbonlimiting algal photosynthesis. High concentrations of free CO(2) are provided through bacterial respiration which is the main contributor to algal photosynthesis. At high photosynthetic activities and low organic loadings, free CO(2) concentrations are low; its flux into algal cells determines photosynthesis and biomass production rate in the pond.

No 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.