The potential of sustainable algal biofuel production using wastewater resources

Heterotrophic cultures of microalgae: Metabolism and potential products

Algal–bacterial processes for the treatment of hazardous contaminants: A review

http://www.bashanfoundation.org/gmaweb/pdfs/P-removal.pdf

Recent advances in removing phosphorus from wastewater and its future use as fertilizer (1997-2003).

Production and harvesting of microalgae for wastewater treatment, biofuels, and bioproducts

Microalgal cultures offer an interesting alternative for waste water treatment (urban, industrial or agricultural effluents) because they provide a tertiary biotreatment coupled with the production of potentially valuable biomass, which can be used for several purposes. We review the main abiotic, biotic and operative factors playing a role in the cultivation of microalgae. Various types of bioreactors are scrutinized keeping in view that the main limitation upon the type of usable bioreactors is the enormous volume of water to be treated. The choice of suitable microalgae and cyanobacteria is examined in terms of productivity and easiness of harvesting. The possible alternatives to harvesting are also reviewed with an emphasis on immobilized systems. Finally, the need for more research and development is discussed.

Algae and waste water

As part of a program to develop biological wastewatertreatment systems for cold climate areas four strainsof filamentous, mat-forming cyanobacteria isolatedfrom Arctic and Antarctic environments were evaluatedfor their nutrient stripping and growth capabilities. A tropical strain, Phormidium bohneri, known forits excellent performance in wastewater treatment, wasused as a comparison. Experiments were done inartificial media under controlled batch cultureconditions to avoid interactions with indigenousmicroorganisms such as bacteria and protozoa. Theculture medium simulated real effluents containinghigh concentrations of nitrate and phosphate.Temperatures (5, 15 and 25°C) and irradiances(80, 210, 350, 640 and 1470 µmol photon m-2s-1) wereselected according to situations encountered in avariety of field conditions. For all irradiancelevels, growth was satisfactory at 15 and 25 °C,but limited at 5 °C. At 25 °C a satisfactory nitrogen removal rate (3.5and 4.0 mg N L-1d-1) was obtained forone polar strain (Phormidium tenue) and thecontrol P. bohneri. At 15 °C, the bestnitrogen removal rate (3.5 mg N L-1d-1)was measured with P. bohneri while the best ratefor the polar strains was around 2.3 mg NL-1d-1. At 15 °C, a phosphorusremoval rate of 0.6 mg P L-1d-1 wasobtained with P. bohneri and polar strains P. tenue and Oscillatoria O-210. Nitrogen(NO3
-) and phosphorus (PO4
3-)uptake rates increased as a function of irradianceover the range 80 to 350 μmolphoton m-2s-1. Our results indicate thattertiary biological wastewater treatment at lowtemperatures (5 °C) cannot be anticipated withthe polar strains tested, because they arepsychrotrophic rather than psychrophilic and thus growtoo slowly under conditions of extreme cold. However, it appears that these cyanobacteria would beuseful for wastewater treatment at moderately cooltemperatures (c. 15 °C), which are commonduring spring and fall in northern climates.

Nitrogen and phosphorus removal by high latitude mat-forming cyanobacteria for potential use in tertiary wastewater treatment

Chitosan:Phormidium aggregates (chitosan: algae=1:2, dry weight basis) were used as a biological tertiary treatment to remove the nitrogen (NH4+, NO2-, NO3-) and phosphorus (PO43-) from a secondary effluent. In a batch system, 71 and 92% of P−PO43-were removed after 6 and 24 h, respectively. The orthophosphate removal rate was identical for all three concentrations of algae-chitosan tested (3.3, 4.6, 5.9 g d. wt.·l-1), and was 90 μg±2 μg P−PO43-·l-1·h-1, for a 90% removal. Under control conditions (chitosan flakes only added to the effluent) 73 and 78% of PO43-were removed after 6 and 24 h respectively. A 95% removal of inorganic nitrogen (NH4+, NO2-, NO3-) was attained after 4–6 h withPhormidium immobilized on chitosan flakes, as compared to 30% with chitosan flakes alone (5 g d. wt.·l-1). The system gave a similar performance when operated semi-continuously over 5 days at a daily retention time of 1.0. In the presence of chitosan-immobilized algae, medium P−PO43-levels were reduced by 87.3%±6.4% after 24 h (61.1 μg±7.0 μg P·l-1·h-1). The reduction of inorganic nitrogen in the medium was 98% after 24 h (370 μg±50 μg N·l-1·h-1). In the presence of chitosan alone, some 60% orthophosphate removal was recorded, whereas no reduction of nitrogen was observed. Disappearance of orthophosphate was attributed to its co-precipitation with calcium released from the chitosan by abrasion. The presence of the algae protected the chitosan from abrasion andPhormidium directly assimilated the orthophosphate and inorganic nitrogen, thus reducing their levels in the effluent.

Biological tertiary treatment of urban wastewaters with chitosan-immobilized Phormidium

Forty-nine strains of filamentous, mat-forming cyanobacteria isolated from the Arctic, subarctic and Antarctic environments were screened for their potential use in outdoor waste-water treatment systems designed for cold north-temperate climates. The most promising isolate (strain E18, Phormidium sp. from a high Arctic lake) grew well at low temperatures and formed aggregates (flocs) that could be readily harvested by sedimentation. We evaluated the growth and nutrient uptake abilities of E18 relative to a community of green algae (a Chlorococcalean assemblage, denoted Vc) sampled from a tertiary treatment system in Valcartier, Canada. E18 had superior growth rates below 15°C Canada. (µ = 0.20 d-1 at 10°C under continuous irradiance of 225 µmol photon m-2 s-1) and higher phosphate uptake rates below 10°C (k = 0.050 d-1 at 5°C) relative to Vc (µ=0.087 d-1 at 10°C and k = 0.020 d-1 at 5°C, respectively). The green algal assemblage generally performed better than E18 at high temperatures (at 25°C, µ = 0.39 d-1 and k = 0.34 d-1 for Vc; µ = 0.28 d-1 and k = 0.33 d-1 for E18). However, E18 removed nitrate more efficiently than Vc at most temperatures including 25°C. Polar cyanobacteria such as strain E18 are appropriate species for waste-water treatment in cold climates during spring and autumn. Under warmer summer conditions, fast-growing green algae such as the Vc assemblage are likely to colonize and dominate, but warm-water Phormidium isolates could be used at that time.

D. Proulx

Papers

Algae and waste water

Nitrogen and phosphorus removal by high latitude mat-forming cyanobacteria for potential use in tertiary wastewater treatment

Biological tertiary treatment of urban wastewaters with chitosan-immobilized Phormidium

Polar cyanobacteria versus green algae for tertiary waste-water treatment in cool climates

Effects of a bacterial biofilm on intensive Daphnia culture