Urban wastewater contains both organic and inorganic nutrients and discharge of untreated water increases nitrogen and phosphorous content in water bodies leading to eutrophication problem. Physical and chemical treatment of urban waste water produces large quantities of waste sludge associated with secondary pollution. Microalgae can assimilate nutrients especially nitrogen and phosphorous from wastewater for their growth and produce valuable biomass and lipid. This study was performed to determine the growth of Chlorella vulgaris in urban wastewater (UWW) and Bold’s basal medium (BBM) thereby identifying cost effective growth medium for microalga cultivation. In addition, nutrient removal abilities of C. vulgaris from various dilutions of urban waste water were explored at 10 days cultivation period. Specific growth rate, biomass and lipid content were higher in microalgae grown in urban waste water than BBM. The highest lipid productivity of 14.31 mg · L−1·day−1 was achieved in the culture grown in UWW medium which exceeded the BBM at 1.15 fold. The amount of nutrient removal tended to increase with higher dilutions of UWW. Removal rates of upto 87.9% and 98.4% were recorded for total nitrogen and total phosphorous by C. vulgaris. The results emphasized that urban waste water as a cost effective growth medium for higher biomass and lipid production accompanied with the nutrient removal efficiency of microalgae to reduce eutrophication.
Increasing industrialization and population explosion result in contamination of wastewater with available water resources. Discharge of urban waste water into water bodies introduces high levels of nitrogen and phosphorous which leads to eutrophication. Nutrient removal is an important aspect of wastewater treatment as eutrophication causes oxygen depletion in aquatic environments, increase in undesired vegetation, loss of aquatic flora and fauna. Phosphorous removal from waste water includes chemical treatment followed by physical treatment; however this method produces large quantities of waste sludge. Algae induced chemical processes are used to eliminate nitrogen and phosphorous [
Microalagae are used to treat various wastewaters in recent times [
Urban waste water (UWW) was collected from Bangalore and was characterized in terms of pH, electrical conductivity, temperature, biological oxygen demand, chemical oxygen demand, total organic carbon, total nitrogen and total phosphorous using APHA method [
Species of Chlorella, Scenedesmus, Pandorina and Oscillatoria were the major isolates identified and cultivated using urban waste water as scale up medium for a period of 6 days at 24˚C ± 2˚C under illumination (12 h light/12 h dark). Chlorella vulgaris was selected and used for further studies as this strain could achieve relatively high biomass concentration among other isolates when cultivated in urban wastewater.
Both Urban Waste Water (UWW) and Bold’s Basal Medium (BBM) were used to determine the influence of growth medium on microalgal growth. Various parameters such as specific growth rate, biomass concentration, pigment concentration, total proteins and carbohydrates content and lipid productivity were determined. All experiments were performed in triplicates and the average values were statistically analyzed.
Specific growth rate (μ·d−1) of the microalgae was calculated according to the following formula [
where, Nt and N0 are the dry cell weight concentration (g·L−1) at the end (Tt) and start (T0) of log phase respectively.
Biomass (g·L−1) of C. vulgaris grown in waste waster medium and BBM was determined by measuring the optical density of samples at 600 nm (OD600) using UV-Vis spectrophotometer. Biomass concentration was then calculated by multiplying OD600 values with 0.6, a predetermined conversion factor obtained by plotting OD600 versus dry cell weight (DCW). DCW was determined gravimetrically by centrifuging the algal cells (3000 × g, 10 min) and drying.
The biomass productivity (g·L−1·d−1) was calculated according to Equation (2),
where Bt was the final biomass concentration, B0 is the initial biomass concentration and d is the cultivation time.
Cellular pigments were determined using a spectrophotometric method after extraction with 80% acetone [
Subsequently, the amount of pigments was calculated using the following formulae
where Ca is the chlorophyll a, Cb is the chlorophyll b, and Ct is the total carotenoids (µg·mL−1).
The extraction of proteins from microalgae was performed using alkali method. Aliquots of algal sample were centrifuged and 0.5 N NaOH was added to the pellet followed by extraction at 80˚C for 10 mins. The mixture was centrifuged and protein content of the supernatant was estimated using Bovine Serum Albumin (BSA) as standard [
Cellular carbohydrates were estimated using the anthrone method [
Lipid extraction from dried algal cells were carried out by chloroform:methanol extraction method [
where m1 is the weight of the dried algal cells, m0 is the weight of the empty new screw cap tube and m2 is the weight of the new screw cap tube with the dried lipids.
Lipid productivity (g·L−1·d−1) was determined using the following Equation (4).
Urban waste water was diluted with three initial dilutions (10%, 20% and 30%) using distilled water to determine the nutrient removal efficiency of Chlorella in batch experiments for a period of 10 days. The contents of total phosphorous (P) and total nitrogen (N) before and after the cultivation period were determined [
The urban wastewater was characterized for its physicochemical properties and the pH, electrical conductivity and temperature were 6.6 ± 0.13, 2.314 (mS·cm−1) and 30˚C. The COD, BOD and TOC of the wastewater were 697 ± 14.15 mg·L−1, 974 ± 22.04 mg·L−1 and 257 ± 27.98 mg·L−1. The total nitrogen and phosphorous were 192.27 ± 0.16 mg·L−1 and 39.97 ± 6.7 mg·L−1.
Microalgae isolated from natural environments could adapt better and produce good results [
Parameters | Bold’s basal medium | Urban waste water |
---|---|---|
Specific growth rate (µ d−1) | 1.12 ± 0.03 | 1.06 ± 0.02 |
Total chlorophyll (mg·L−1) | 11.36 ± 0.92 | 9.37 ± 0.54 |
Total carotenoids (mg·L−1) | 4.7 ± 0.10 | 4.8 ± 0.97 |
Total protein (mg·L−1) | 58.7 ± 0.56 | 63.7 ± 1.76 |
Total carbohydrates (mg·L−1) | 196 ± 1.64 | 187 ± 3.61 |
Biomass (g·L−1) | 1.09 ± 0.04 | 1.13 ± 0.02 |
Biomass productivity (g·L−1·d−1) | 0.17 ± 0.03 | 0.19 ± 0.01 |
Lipid content (% DW) | 7.52 ± 0.31 | 8.31 ± 0.35 |
Lipid productivity (mg·L−1·d−1) | 12.38 ± 1.01 | 14.31 ± 0.38 |
Basal Medium (1.09 g·L−1 and 0.17 g·L−1). This scenario was different with specific growth rate i.e. 1.12 µ·day-1 was observed in BBM where as it was 1.06 µ·day−1 in UWW. C. vulgaris has produced a biomass of 2.7 g·L−1 in urban waste water [
For lipid contents, no statistically significant differences between the UWW and BBM were observed. However, the volumetric lipid productivities of the cultures grown in UWW were enhanced notably due to their high cell density. The highest lipid productivity of 14.31 mg·L−1·day−1 was achieved in the culture grown in UWW medium which exceeded the BBM at 1.15 fold. In a study using artificial wastewater medium by Feng et al., [
Urban waste water contains both organic and inorganic phosphate which can be readily assimilated by algae. Phosphorus (P) is an important macronutrient for microlalgal growth and microalgae assimilate phosphorus as inorganic orthophosphate for production of phospholipids, ATP and nucleic acids [
Initial concentration (mg/l) | Final concentration (mg/l) | |||
---|---|---|---|---|
Total N | Total P | Total N | Total P | |
10% | 21.37 ± 0.25 | 1.84 ± 0.22 | 3.61 ± 1.31 | 0.12 ± 0.04 |
20% | 37.46 ± 1.62 | 4.12 ± 0.14 | 7.25 ± 0.47 | 0.09 ± 0.06 |
30% | 59.31 ± 2.74 | 9.61 ± 1.23 | 7.14 ± 2.54 | 0.15 ± 0.03 |
dilutions of wastewater was prepared using distilled water. Both nitrogen and phosphorous removal amounts in different initial concentrations of UWW for 10 days cultivation are represented in
The total nitrogen removal efficiencies recorded were 83.1% ± 0.14%, 78.3% ± 0.06%, 87.9% ± 0.11% in 10%, 20% and 30% dilutions. Up to 84.11% nitrogen uptake from urban waste water was reported by Chlorella [
The results clearly emphasized that urban waste water is a cost effective growth medium for higher biomass and lipid production in microalgae. The nutrient removal efficiency by C. vulgaris isolated from wastewater proved that microalgae are potential in removing nitrogen and phosphorous from highly concentrated nutrient rich urban wastewater. This study highlights the more effective alternative ecofriendly approach for wastewater treatment using microalgae to eliminate eutrophication.
Singh, R., Birru, R. and Sibi, G. (2017) Nutrient Removal Efficiencies of Chlorella vulgaris from Urban Wastewater for Reduced Eutrophication. Journal of Environmental Protection, 8, 1- 11. http://dx.doi.org/10.4236/jep.2017.81001