Algal single cell protein from wastewater treatment and renovation process

Abstract

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.

A review of the harvesting of micro-algae for biofuel production

“…Up to the late 1970s no polyelectrolyte flocculant effective for micro-algal effluent was available (Moraine et al 1979), but effective polyelectrolytes were later found (Shelef et al 1984a). Cationic polyelectrolytes are now considered as the most effective flocculants for the recovery of microalgae (Uduman et al 2010).…”

“…Flocculation and froth flotation has been found to be effective in the removal of micro-algae from wastewater using fine air bubbles (no dimensions given) generated by a sparger with gas pressure of 3 atmospheres (Moraine et al 1979). …”

“…Additional challenges of algae harvesting come from the small size of micro-algal cells (most algae are below 30µm) (Molina Grima et al 2003); the similarity of density of the algal cells to the growth medium (Reynolds 1984); the negative surface charge on the algae that results in dispersed stable algal suspensions, especially during the growth phase (Edzwald 1993;Moraine et al 1979;Packer 2009); and the algal growth rates which require frequent harvesting compared to terrestrial plants .…”

Organic Waste Recycling

“…However from a practical point of view, the depth should be greater than 20 cm (i.e. 40-50 cm) to allow for the sludge layer and for maintaining the needed HRT (Moraine et al 1979). …”

Energy Balance of Biogas Production from Microalgae: Effect of Harvesting Method, Multiple Raceways, Scale of Plant and Combined Heat and Power Generation

“…Achieving an energy return based on the production of biodiesel alone is extremely challenging, however, with 50% of studies on microalgal biodiesel reporting an EORI of <1 [10][11][12][13]. Anaerobic digestion of wet microalgae is potentially an energetically more favourable option as it utilises the entire biomass and does not require drying before digestion [9,[14][15][16] One of the major challenges in achieving an energy return from the production of biofuel from microalgae is harvesting and concentrating the algae [3,17,18]; this is due to a number of factors including the dilute nature of the algal suspension at 0.02%-0.05% dry solids [19,20]; the small size of micro-algal cells (most algae are below 30 µm) [21]; the similarity in density of the algal cells to that of the growth medium [22]; and the negative surface charge on the algae that results in dispersed stable algal suspensions [23][24][25].…”