Peer Reviewed Journal: Treatment of Domestic and Industrial

Pages: 10 (2926 words)  ·  Style: IEEE  ·  Bibliography Sources: 10  ·  Level: Doctorate  ·  Topic: Transportation - Environmental Issues  ·  Buy This Paper

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[. . .] 600ml of wastewater collected (after preliminary screening, free of grit and primary sediments) served as a bacteria inoculums and a supplier for nutrients. Then, cultivation of the settle-able algal-bacteria took place under laboratory conditions of around 190 C. The photo-bioreactor (for culture enrichment) comprised of a transparent PVC 40cm deep and 29 cm in diameter [3].

Therefore, in estimation, the volume of the medium in the reactor was 14 liters. In addition, the constant mixing, using a magnetic stirring bar, done was to avoid sedimentation of the algae. The tank got radiations from two fluorescent lamps for 12 hours each day. For cultivation of the settle-able algal-bacteria culture to occur, the regular mixing stopped for every 23 hours for an hour and discarded the floating biomass, with a screen. Afterwards, 600ml of the wastewater was replaced after three days in order to uphold a continuous supply of nutrients [3]. After one month of cultivation, there was formation of pea green micro-algae, which had an even distribution in the reactor.

Experimental operation

The same reactor utilized for this research, assisted during the batch mode. However, in this case, the pretreated wastewater served as the feed for the reactor unless stated otherwise. Before beginning the batch experiment, algal-bacterial settled differently: by halting the stirring for 30 minutes. In addition, after every eight days, there was a replacement of 12.5litres of the suspension, with fresh water. The fluorescent lamps provided radiations similarly as in the first experiment, and the photoperiod was 12 hours of light and a 12-hour dark phase. In addition, there was a collection, midway, of 150 samples for further evaluation 4 hours after starting the lighting period.

Results and Discussion

Investigation of the settle-ability of the algal-bacteria culture showed good settle ability because all the biomass settled to the bottom of the glass cylinder within a timeline of twenty minutes, resulting in a decrease of TSS from 1.84-0.016 g/l. The resulting sludge ratio was 12%, showing good settle-ability. The god settle-ability was because of the special cultivation approach in this research. In addition, the interchange in mixing and non-mixing activity in the cultivation period enhanced the choosing of settle-able algae and bacteria providing an efficient way of harvesting algal-bacterial biomass [8]. The harvesting using this technique has three advantages; firstly, there was a reduction in the operating cost because the process did not need extra energy or equipment.

Secondly, there was no addition of chemicals hence elimination of secondary pollutants. Lastly, the settle-ability was applicable for a long-term activity. Sedimentation characterized the cultivated algal-bacterial culture, which did not depend on any immobilization medium. The appearance of the algal-bacteria flocs in the reactor shows that the presence of blue-green algae. In addition, the attachment of wastewater filaments to the algae forms a cooperative system. The cooperation provides support for bio-flocculation leading to the development of settle-able biomass [9]. Several factors such as algae cell surface properties, extracellular polymeric substances, and cations influenced formation and stability of the settle-able algal-bacterial biomass.

Temperature, dissolved oxygen and pH

The variation in temperature, pH and dissolved oxygen had some influence on the treatment process. For instance, the culture temperature, at the start of the process was 12 degrees Celsius. This was probably because of addition of wastewater into the bioreactor after collecting the wastewater. There increase of temperature to room temperature, but remained constant until the end of each batch test. In addition, at the start of the test, dissolved oxygen (DO) was the same compared to the pre-treated water. However, when running the batch test, dissolved oxygen (DO) values reduced to around zero.

This indicated that there was consumption of oxygen generated from the algal photosynthesis, by nitrification, and heterotrophic carbon dioxide oxidation. However, after three days, there was a gradual increase in the levels of oxygen at the end of each test. Additionally, there was no substantial variation in culture pH during the batch tests detected [9]. However, there was a slight pH reduction because of intensive nitrification after the five days. Afterwards, there was a gradual increase in pH. Factors such as micro-algal growth, nitrification, and excretion of basic metabolites due to biodegrading of organic matter have significance influence on pH [3].

Elimination of phosphate

Removal phosphate was a slow process as compared to that in nitrogen. This may probably because nitrogen was the limiting nutrient and not phosphate in this system. Earlier studies show that the optimal ratio for maximum uptake of nitrogen and phosphorous, by algal-bacterial culture is N: P= 30:1. However, for this study, the ratio was far much lower as compared to the optimal ratio [3]. Additionally, an investigation on the balance of phosphorous showed that phosphorous remained the primary mechanism in the system. Elimination of phosphorous is possible through assimilation of biotic phosphorous into the biomass and biotic phosphorus precipitation, which takes place in the form of orthophosphate precipitation at a higher pH.

Elimination of nitrogen

Nitrogen influent was primarily in the form of N-NH+4 (70-90%), N-NH+4 removal effectiveness for all the tests were approximately 100%, while the removal efficiency of TKN varied from 76.6%-97.8%. However, for the last two tests, TKN removal efficiency was low compared with that in the previous two batches. In addition, there was still some amount of organic nitrogen in the wastewater [10]. The organic nitrogen was because of the small amounts of inseparable organic matter generated during the growth of algae and treatment of wastewater. In addition, incipient nitrification account for the presence of N-NO3- around 5.2mg/l. An investigation on the balance to understand the nitrogen removal mechanism show that, the total removal of nitrogen and concentration of biomass accounted approximately for 0.3%, 0.4%, 0.5% and 0.4% of the total nitrogen in the four batches [3]. Contribution of the volatilization of ammonia in the removal of nitrogen is negligible because of the low ammonia concentrations and relatively low pH.

Conclusion

The analysis presented in this paper shows that algae-based treatment is efficient in control of water pollution. The algae evidently show that it is possible to treat domestic wastewater, industrial wastes, and agricultural wastes. In addition, from the review part, it is apparent that algae can improve water quality. Therefore, algae play a significant role in the purification of wastewater. However, temperature, biological activity and flow rate greatly influences nutrient removal. A settle-able algal-bacterial culture, cultivated from wastewater shows evidence that it can successfully treat wastewater stirred in a tank bioreactor. In addition, the algal-bacterial, while it was possible to reduce the total suspended solid to o.o16g/l in a timeline of 20 minutes.

The average removal of COD, TKN and phosphate were 1.3% 1.6% and 1.0% in a timeline of eight days respectively. Additionally, the average mass generation was 1.2g/m2 .d. It is important to note that, in this study, it is apparent that biomass uptake was the main process involved in removal of nutrients. The primary algae species in the bioreactor was blue-green algae, and the primary bacteria present in the photo bioreactor included Flavobacteria, Gammaproteobacteria. Bacteroidia and Betaproteobacteria. This paper review provides a new insight into settle-able algal-bacteria culture enrichment strategies and greatly contributes to microbial ecology and diversification in algal-bacterial culture.

References

1. A. Dixit, A. Dixit, S. Dixit, & C.S. Goswami, "Process and Plants for Wastewater Remediation: A Review," Scientific Reviews and Chemical Communications, Vol. 1, Issue 1, pp. 71-77, 2011.

2. M. Johnson, & D.D. Mara, "Aerated Rock Filters for Enhanced Nitrogen and Fecal Coli form Removal from Facultative Waste Stabilization Pond Effluents, "Water Science and Technology, Vol. 51, Issue 12, pp. 99 -- 102, 2005.

3. Oligae, (2013, January) Guide to Algae-based Wastewater Treatment: A Sample Report. Oligae. India. [Online]. Available from https://secure.clixoo.com/purchase/oilgae/wwt/report.html

4. Y. Su, A. Mennerich, & B. Urban, "Municipal Wastewater Treatment and Biomass Accumulation with a Wastewater-born and Settleable Algal-Bacterial Culture," Water Research, Vol. 45 pp. 3351-3358, 2011.

5. N. Mallick, "Biotechnological Potential of Immobilized Algae for Wastewater N, P and Metal Removal: A Review," Biometals, Vol. 15, Issue 4, pp. 377-390, 2002.

6.A.F. Barsch, "Algae as a Source of Oxygen in Waste Treatment," Journal of the Water Pollution Control Federation, Vol. 33, issue 3, pp. 239 -- 249, 1961.

7 C.E. Boyd, "Accumulation of Dry Matter, Nitrogen and Phosphorus by Cultivated Water Hyacinths," Econ. Bot, Vol. 30, pp. 51-56, 1976.

8 T.J. Hurse, and M.A. Connor, "A Contour Approach that Uses Data Accumulated During Routine Monitoring to obtain Insights into Lagoon Behavior," Water Science and Technology, Vol. 42, Issue… [END OF PREVIEW]

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