Comparative study for Treatment of Domestic Wastewater Using Chlorella Vulgaris

Tertiary treatment using chemicals frequently prompts secondary contamination of sludge, making other issues of safe disposal. Thus, vitality and cost required for tertiary treatment of wastewater stay an issue for industries and municipalities. In this study, different microalgal concentrations (20%, 25%, 30%, 35%, 40% and 45%) were studied to treat domestic wastewater at 11 hours HRT for both ltered and non-ltered euent. During the study, removal was observed in Total Solids (TS), Total Dissolved Solids (TDS), Total Suspended Solids (TSS), Electrical Conductivity (EC), phosphate, ammonia and COD for all the microalgal concentrations mentioned. However, the maximum removal eciency was observed at 30% microalgal concentration. Maximum removal eciency found in ammonia, phosphate and COD for non-ltered euent was 96.60%, 91.73% and 84.71% respectively, whereas, in the case of the ltered sample, removal eciency reached up to 97.62%, 92.47% and 88.75% for ammonia, phosphate and COD respectively. In the case of solids (specically TSS) and EC, removal eciency reached up to 30.87% and 24.31% respectively for non-ltered euent and was 48.00% and 25.88% in the ltered sample. The study showed that an algae-based system could accomplish more affordable and environment-friendly way to treat domestic wastewater without tertiary treatment to a desirable limit. and 810 mL (45%) while the remaining volume was made up by the raw domestic wastewater collected from the nearby sewage pumping station at Surat. The study was conducted in an open atmosphere under natural light conditions. External aeration was provided for 10 hours to keep microalgae in suspension, followed by an hour of settling. After the settling period, the supernatant was drawn for physico chemical analysis. The time slot for an 11-hour study was 10:00 hours – 21.00 hours, which has both the effect of light and dark phase. The light intensity during this phase was about 6 hours. The study was conducted in a pair of different microalgal concentration, i.e., 20% and 25%, 30% and 35%, 40% and 45%. Various parameters analyzed during the study (for both the phase) were pH, Electrical Conductivity (EC), Total Dissolved Solids (TDS), Total Solids (TS), Total Suspended Solids (TSS), Chemical Oxygen Demand (COD), phosphate, ammonia, nitrate and Dissolved Oxygen (DO) as prescribed in APHA, 2012 manual. During the initial phase of the study, a faint green tint was observed in the euent due to the presence of lamentous algae. But with the time, the microalgal settleability improved and the intensity of color decreased to nil. Hence the study was also conducted with the euent, ltered with a coarse lter (4-5.5 µm) to get an idea about the color impartment. The study was


Introduction
The world will confront 40% water de ciency by 2030, which is a challenge for sustainable development [1,2]. This shortfall may emerge from the expanding interest for water, degradation of water assets and the absence of innovations to recover the used water. Water contamination is a joined after effect of various anthropogenic exercises [3]. The untreated wastewater contains uctuating degrees of organic and inorganic mixes. The deterioration of water quality when the sewage is discharged into receiving bodies would likewise prompt water shortage, which is a signi cant issue far and wide. Sewage is the conversion of 70-80% of the total water supplied for domestic purpose, of different chemical compositions with varying quality and quantity, depending on the source.
In India, 61,754 MLD is the sewage generated against the sewage treatment capacity of 22,963 MLD, owing to the distinct gap between sewage generation and treatment capacity, about 38,791 MLD of untreated sewage (62% of total sewage) is directly discharged into nearby water channels [4]. The wastewaters originating from these point or nonpoint sources, if disposed of in a nearby water body without any treatment, adversely affect the water quality and aquatic ecosystem [5]. Thus, the current need is to minimize the consumption of water as well as to return it to the earth with minimum possible pollution because of the limited potential of self-puri cation in water bodies [6].
However, most existing sewage treatment processes in developing countries are confronting di culties with nitrogen and phosphorus removal to meet the necessities for disposal and water reuse. Conventional nutrients removal methods, such as activated sludge-based treatment process, nitri cation-denitri cation, chemical phosphorus removal, and coagulating sedimentation are facing di culties in meeting the stringent nutrient release guidelines effectively at low expenses [4,7]. Besides, their downsides, for example, high vitality utilization, imsiness treatment impact, long procedure, carbon emanation, excess sludge discharge are additionally obvious obstructions to coordinate the idea of the practical advancement in wastewater treatment with low-carbon, low vitality utilization and asset reusing [8,9].
The most eco-friendly and economical technique for wastewater treatment is with biological methods, where chemical break down and treatment of residues is done by microorganisms also with the production of added-value compounds [10,11]. Many studies have proposed microalgae as an alternative biological treatment that e ciently removes nutrients from wastewater [12] even when nutrient concentrations are high [13][14][15][16]. Wastewater treatment using microalgae was rst described in early 1950s. The term "phycoremediation" was coined by John in 2000 to address bioremediation carried out by algae. Municipal wastewater is enriched with a substantial amount of ammonia, phosphate and other essential nutrients which support algal biomass production [17,18].
Literatures have been reported with nitrogen (> 90%) and phosphorus (> 50%) removal using microalgae [11]. Chlorella vulgaris can effectively remove nitrogen (up to 81-85%) and phosphorus (32-36%), respectively [19], Galdieria sulphuraria when used removed ammonia nitrogen (63-89%) and phosphorus (71-95%), respectively [20]. The green algae Micractinium sp. when used for nutrient removal, it gave e ciency to the system about > 90% in the case of both phosphorus and nitrogen respectively [13].In the present study, an attempt was made to analyze the effectiveness of the microalgal system if incorporated in wastewater treatment regarding the removal of the different physico-chemical parameters along with nutrients at much lesser Hydraulic Retention Time (HRT) in the Indian context.

Materials And Methods
Nutrient and organic removal batch study was performed using Chlorella vulgaris in 2L glass beakers with a working volume of 1800 mL at 11 hours HRT as shown in Fig. 1. Different glass beaker with varying microalgal concentrations 360 mL (20%), 450 mL (25%), 540 mL (30%), 630 mL (35%), 720 mL (40%) and 810 mL (45%) while the remaining volume was made up by the raw domestic wastewater collected from the nearby sewage pumping station at Surat. The study was conducted in an open atmosphere under natural light conditions. External aeration was provided for 10 hours to keep microalgae in suspension, followed by an hour of settling. After the settling period, the supernatant was drawn for physico chemical analysis. The time slot for an 11-hour study was 10:00 hours -21.00 hours, which has both the effect of light and dark phase. The light intensity during this phase was about 6 hours. The study was conducted in a pair of different microalgal concentration, i.e., 20% and 25%, 30% and 35%, 40% and 45%. Various parameters analyzed during the study (for both the phase) were pH, Electrical Conductivity (EC), Total Dissolved Solids (TDS), Total Solids (TS), Total Suspended Solids (TSS), Chemical Oxygen Demand (COD), phosphate, ammonia, nitrate and Dissolved Oxygen (DO) as prescribed in APHA, 2012 manual. During the initial phase of the study, a faint green tint was observed in the e uent due to the presence of lamentous algae. But with the time, the microalgal settleability improved and the intensity of color decreased to nil. Hence the study was also conducted with the e uent, ltered with a coarse lter (4-5.5 µm) to get an idea about the color impartment. The study was conducted to analyze the sustainability of the microalgae system to have the effect of both light and dark phases when used in an actual scenario.

Results And Discussion
During the experimental process, various physico chemical parameters were measured at 11 hours HRT for all the concentrations of C. vulgaris (20%, 25%, 30%,35%, 40% and 45%). The average concentration of raw domestic wastewater collected from a nearby sewage pumping station for various parameters studied is tabulated in Table 1.
After the treatment of the raw domestic wastewater with microalgae, it was found that even though with low HRT of 11 hours in the present study, e cient removal was observed in all the parameters analysed at different microalgal concentration when compared with various literatures where the HRTs varied in days to weeks [21][22][23]. Chlorella vulgaris was used because of its characteristics features like (1) high growth rate, (2) fast nutrient removal rate; (3) strong adaptability to different types of wastewater and local climate; and (4) high biomass productivity [1].After the treatment of the raw domestic wastewater with microalgae, it was found that coupling WWT with algae can be a reasonable, cost-effective viable opportunity for water treatment, with an opportunity for clean water production in areas of water scarcity [24]. Removal in different parameters was observed in each concentration studies. However, maximum removal was found in the e uent of the 30% microalgae.
Nitrogen is transformed into N 2 gas in conventional nitrogen removal methods, whereas in the algal treatment system, nitrogen compounds are taken up for their growth [25]. The uptake of nitrate is light energy-dependent, and also microalgae prefer to utilize already reduced nitrogen, such as ammonium in comparison to nitrate, which is less energy intensive conversion [26]. Ammonia was e ciently removed in the system as it is incorporated into protein via protein anabolism for microalgal growth [27,28] Fig. 2(a). Increase in nitrate concentration was observed during the study as ammonia was converted to nitrate in aerobic condition via nitri cation [29].
Microalgae have also shown the great potential to utilize phosphorus from wastewater, but mainly in the form of orthophosphate [30], and it is incorporated into organic compounds such as nucleic acids, phospholipids and proteins [31]. Variation in percentage removal e ciency for phosphate at different concentration considered in the study was 60.  Fig. 2(b).
COD removal is performed in the microalgae system in symbiotic relation with the heterotrophic bacteria [32], as the oxygen produced by algae as an end product is utilised by bacteria for their growth and survival [33] Fig. 3.
During the study, removal in TS and TSS was also observed to a certain extent due to the formation of algal bacterial biomass that settles down and leaves a clear supernatant. Variation in percentage removal e ciency for TS at different microalgal concentration considered in the study was 11.74 ± 7.2 for 20% concentration, 12.36 ± 6.6 for 25% concentration, 13.72 ± 4.13 for 30% concentration, 11.14 ± 4.85 for 35% concentration, 11.23 ± 4.77 for 40% concentration and 11.53 ± 5.00 for 45% concentration in case of non-ltered e uent. However, when e uent was ltered with a coarse lter to remove lamentous microalgae, removal e ciency further increased to 18.17 ± 6.71 for 20% concentration, 17.64 ± 6.71 for 25% concentration, 22.27 ± 5.68 for 30% concentration, 19.98 ± 6.62 for 35% concentration, 18.44 ± 5.52 for 40% concentration and 18.69 ± 5.51 for 45% concentration as shown in Fig. 4(a). Variation in removal e ciency for TSS at different concentration considered in the study was 15.28 ± 11.65 for 20% concentration, 16 Fig. 4(b). The problem of separating algae from water may be solved by using attached algae because these attached algae are often observed in the form of algal bio lm in su cient sunlight [34].
Microalgal system lead to increase in DO concentration, which raised up to 6.6 mg/L, 6.8 mg/L, 7.2 mg/L, 7.6 mg/L, 7.6 mg/L and 7.8 mg/L respectively when in uent was treated with microalgal concentration of 20%, 25%, 30%, 35%, 40% and 45% respectively. The increase in DO was mainly because of the photosynthetic effect of algae in addition to external aeration provided for the mixing of algae in the in uent. Algal growth increases alkalinity to a remarkable level regardless of the initial pH [35]. The rise of pH by photosynthesis was impeded due to the production of H + ions by nitri cation and by the use of ammonium as a nitrogen source for the photosynthesis process itself [36]. The elevated pH also

Conclusions
Algal treatment of wastewater, mediated through a combination of nutrient uptake, raised pH and high dissolved oxygen concentration, can offer an ecologically safe, cost-effective and e cient means to expel nutrients than conventional tertiary treatment. The study found that 30% concentration of Chlorella vulgaris is the optimum concentration among all the concentration studied to remove the nutrients, organic content and solids effectively with maximum removal e ciency greater than 90% without causing secondary sludge unlike other conventional and chemical treatments used for domestic wastewater treatment. Algae in wastewater can signi cantly contribute to the management of freshwater ecosystems by providing a more environmentally sound approach to deal with lessen eutrophication capacity of the point source.