Bioflocculent algal–bacterial biomass improves low-cost wastewater treatment

Abstract

An innovative technology for the biological treatment of wastewater in regions with sufficient solar radiation based on the simultaneous growth and degradation processes of algal and bacterial biomass is presented. The aim of the work is the improvement of pond technology through the formation of stable algae-bacteria aggregates, which a) permit a simple separation of the algal biomass by gravity sedimentation, b) enable a high removal efficiency for organic carbon and nutrients, and c) are independent in terms of oxygen provision through algal photosynthesis. Algae-bacteria aggregates could be developed with a suitable algal species (Chlorella vulgaris, Strain Hamburg) as a 'model organism' in a wastewater environment. The morphology of algal-bacterial flocs is similar to activated sludge flocs. They are stable and settle quickly. Floc size ranged between 400 and 800 microm. Results of our experiments with an artificially irradiated lab-scale system, operated in continuous flow mode, revealed that even at a relatively short hydraulic detention time of two days, a high elimination capacity of 9.96 g N m(-2) d(-1) and 0.87g Pm(-2) d(-1) can be achieved. Recent investigations confirmed that floc formation of unicellular algae and wastewater bacteria also could be developed and maintained in a pilot-scale system with a water depth of 0.5 m.

Bioflocculation for Control of Wastewater Pond Microalgae

“…Like bacterial sludge, algal sludge is rich in recovered nutrients, has the potential to be used as fertilizer, and can be anaerobically digested to recover biogas energy (Benemann et al, 1996;Gutzeit et al, 2005). Unlike wastewater bacterial sludge, algae biomass has high crude protein content (~50%) and could be used as animal feed with the proper processing.…”

“…• Promoting growth of cyanobacterial scums, which are an operational nuisance Although pond systems typically require lower costs than mechanical systems, high effluent suspended solids concentrations can prevent some pond systems from being a feasible treatment technology (Gutzeit et al, 2005). Algal suspended solids can be removed from pond effluents by addition of advanced processes such as coagulation followed by flotation or centrifugation, but these more than double the capital and operations cost of advanced pond systems (Downing et al, 2002).…”

“…Aerobic heterotrophic bacteria, responsible for oxidizing influent BOD, use dissolved oxygen as their electron acceptor and produce water and carbon dioxide as byproducts (Metcalf and Eddy, 2003). Water, carbon dioxide from cellular respiration, and solar energy from the sun is then used for photosynthesis that occurs in the chloroplasts of algae cells (Gutzeit et al, 2005). An additional benefit of producing algae is that they contribute to nitrogen and phosphorus removal by assimilating ammonium and phosphates during growth (Oron et al, 1979;Gutzeit et al, 2005) Natural systems are most favorable for warm-climate communities with available land for construction (Oswald, 1990;Gutzeit et al, 2005;Kaya et al, 2007).…”

“…Water, carbon dioxide from cellular respiration, and solar energy from the sun is then used for photosynthesis that occurs in the chloroplasts of algae cells (Gutzeit et al, 2005). An additional benefit of producing algae is that they contribute to nitrogen and phosphorus removal by assimilating ammonium and phosphates during growth (Oron et al, 1979;Gutzeit et al, 2005) Natural systems are most favorable for warm-climate communities with available land for construction (Oswald, 1990;Gutzeit et al, 2005;Kaya et al, 2007). In addition to their aesthetic appeal, natural systems have the following advantages (Benemann et al, 1980;Crites and Tchobanoglous, 1998;Green et al, 1995;Kaya et al, 2007;Oswald, 1990 (Metcalf and Eddy, 2003).…”

“…Algal photosynthesis provides oxygen to the organotrophs responsible for oxidizing the influent organics and nitrifiers, which are responsible for oxidizing influent ammonia to nitrite and nitrate (Gutzeit et al, 2005;Benemann et al, 1996). Large solids settle to the bottom of the ponds and degrade anaerobically (USACE, 1999).…”