Introduction

In recent years, the importance of biological waste treatment systems has caught the attention of workers all over the world and has helped in developing relatively efficient, low cost waste treatment system.  The usefulness of algal systems, more particularly cyanobacteria, in not only treating the wastes but also producing a variety of useful byproducts from their biomass is being understood (Subramanian and Shanmugasundaram, 1983).

Phycoremediation applied to the removal of nutrients from wastewater and other high organic content wastewater is a field with a great potential and demand considering that surface and underground water bodies in several regions of the world are suffering of eutrophication. However, the development of more efficient nutrient removal algal systems requires further research in key areas.

When considering biological wastewater treatment for a particular application, it is important to understand the sources of the wastewater generated, typical wastewater composition, discharge requirements, events and practices within a facility that can affect the quantity and quality of the wastewater, and pretreatment ramifications. Consideration of these factors will allow you to maximize the benefits your plant gains from effective biological treatment.

This study aims to analyse physico-chemical properties of untreated and treated wastewater and to evolve effective and economic biological treatment method for the sewage wastewater using micro algae.

Materials and Methods

Sewage wastewater was collected from the Cooum in Chennai city. In order to select organism for the treatment process, micro algal populations were collected at different places from where the effluent was collected; isolated and identified by using the standard manual (Desikachary,1959)) and were maintained in CFTRI medium (1985).

To study the role of cyanobacteria in sewage water, the following protocols were employed. i) Effluent treated without Oscillatoria sp and Scytonema sp (control) and ii) Effluent treated with Oscillatoria sp and Scytonema sp. Experiments were conducted in duplicates and repeated three times.

. Two ml of uniform suspension of Oscillatoria sp and Scytonema sp were inoculated in each flask containing 2 liter of effluent (i). The experiment was conducted under controlled conditions (temperature 27 ± 2ºC) with a light intensity of 2000 lux, provided from overhead cool light white fluorescent tubes (16L+8D) for a total duration of 15 days. Samples were periodically (every 5^th day) analyzed for various physico-chemical parameters such as pH, carbonate, bicarbonate, calcium, magnesium, sodium, potassium, nitrate, phosphate, chloride, iron, BOD and COD etc., using standard methods (APHA, 2000).

Table 1: Physico-chemical parameters of sewage wastewater treated with Oscillatoria sp.

Table 2: Physico-chemical parameters of sewage wastewater treated with Scytonema sp.

Results and Discussion

The study revealed that the sewage water was blackish in colour with disagreeable odour which may be due to decomposition of organic matter or presence of various aromatic and volatile organic compounds (Singh et al., 1998) due to microbial activity. These changes in colour and odour of the sewage water may be due to the action of algae which decomposed the organic matter present in both untreated and treated sewage water made the water clear and these findings are in accordance with the work (Verma et al., 2002).

Turbidity is a measure of the light-scattering potential of wastewater, caused by the presence of colloidal and suspended material. Effluent filtration can decrease turbidity levels. In the study turbidity was reduced to 65.51 percent by Oscillatoria sp and 86.63 percent by Scytonema sp.

The amount of total solids was reduced to 56.89 percent by when the sewage water was treated with Oscillatoria sp and 58.03 percent when the sewage water was treated with Scytonema sp^.. Veeralakshmi et al., (2007). reported 19.50 percent reduction of total solids when the petroleum effluent was treated with Oscillatoria sp.

Total dissolved solids in the present study were reduced to 56.88 percent when the effluent was treated with Oscillatoria sp and 58.74 percent by Scytonema sp. With regard to TDS, both treated and untreated sewage water were found to contain high levels of TDS compared to the permissible limits of CPCB (1995) and these high levels of TDS may be due to salt content present in the same and also renders it unsuitable for irrigation. Veeralakshmi et al., (2007) reported 19.16 percent reduction of TDS when the petroleum effluent was treated with Oscillatoria sp.

Total suspended solids were reduced to 66.66 percent when the sewage water was treated with Oscillatoria sp and 72.22 percent by Scytonema sp. The total suspended solids were found to be beyond the permissible limit (100 mg/L) of ISI (1979) in the raw sewage water which could lead to various environmental factors like reducing the diversity of aquatic life and in oxygen depletion. The study confirmed that due to reduction of suspended solids the sewage water is suitable for safe disposal on land through irrigation. The untreated sewage water contains a considerable amount of total suspended and total dissolved solids. It is an important parameter (Feign et al., 1991) for evaluating the suitability of the sewage water for irrigation purpose since these solids might clog both the soil pore and components of water distribution system.

Electrical conductivity of the treated sewage water was reduced to 58.79 percent by Oscillatoria sp and 57.13 percent by Scytonema sp. The higher level of electrical conductivity in untreated effluent could be attributed to the use of inorganic chemicals in dairy manufacturing. A high level of conductivity is due to increased concentration of salts. Electrical conductivity were found to be within the permissible limits (3000 μS/cm) issued by irrigation guidelines (Hamoda and Al-Awadii, 1996)

When sewage water was treated with algae the pH was increased and became alkaline, hence, the pH affect the treatment efficiency was investigated. Manoharan and Subramanian (1992b) have also reported that the rise in pH value up to 10^th day of growth. In the present study interestingly, the pH of the sewage water increased to 7.33 by Oscillatoria sp and 7.80 by Scytonema sp. Along the limited nutrients from wastewater for their improvement over growth metabolism, they produce oxygen (Vijayakumar et al.,2005) reported increase of pH in dye effluent, when treated with Oscillatoria sp.

Alkalinity is the capacity of water to neutralize the strong acid, depending upon the capacity of hydroxyl ions to combine with hydrogen ions. Alkaline nature of effluent showed gradual reduction. Alkalinity of the effluent was reduced to 28.26 percent by Oscillatoria sp and 30.43 percent by Scytonema sp. Alkalinity was found to be high which is harmful to aquatic organism (Nemerow, 1978). The bicarbonate affects the uptake and metabolism of nutrients by plants (Richard, 1968)^.  Vijayakumar et al.,.(2005) reported reduction of carbonate in dye effluent, when treated with Oscillatoria sp.

Wastewater treatment processes generally have little effect on the hardness of wastewater. Total hardness was reduced to 71.00 percent when the sewage water was treated with Oscillatoria sp and 75.00 percent by Scytonema sp proving that efficient nutrient uptake of micro algae.  In the present study calcium level was reduced to 72.94 percent when the sewage water was treated with Oscillatoria sp and 75.88 percent by Scytonema sp.  Although, calcium is undoubtedly required for cyanobacterial growth (Fogg, 1973), substantial reduction in calcium level cannot be explained by uptake. Divalent cations such as calcium and magnesium are known to be essential for flocculation and would co-flocculate (Richmond  and Becker, 1986). Similarly the magnesium level was reduced to 75.94 percent when the sewage water was treated with Oscillatoria sp and 80.49 percent by Scytonema sp. Veeralakshmi et al., (2007) reported 53.33 percent of calcium and 52.94 percent magnesium reduction when the petroleum effluent was treated with Oscillatoria sp.

In the present study sodium level was reduced to 47.65 percent when the sewage water was treated with Oscillatoria sp and 53.12 percent by Scytonema sp. Similarly the level of potassium was increased to 25.00 percent when treated with Oscillatoria sp and reduced to 16.66 percent when the sewage water was treated with Scytonema sp. The treated sewage water contains increased amount of potassium was due to the addition of nutrients in the treatment process (Somashekar, 1984)^. Veeralakshmi et al.,(2007) reported 57.50 percent of sodium and 33.33 percent potassium reduction when the petroleum effluent was treated with Oscillatoria sp.

Iron content in the present study was increased to 79.06 percent when the effluent was treated with Oscillatoria sp and 92.62 percent by Scytonema sp. Most of algal forms occurring in the polluted fields have well defined sheath.  Only the ensheathed forms of blue-green algae were found tolerating high concentrations of industrial effluents in laboratory culture (Adhikary, 1985; Adhikary and Sahu, 1988). Thus it is fairly convincing that these outermost surface structures play an important role for making ensheathed forms of blue green algae to thrive in adverse conditions.  Veeralakshmi et al.,,(2007) reported 87.47 percent reduction of iron when the petroleum effluent was treated with Oscillatoria sp.

The specific use of cyanobacterium in the efficient removal of different forms of combined nitrogen and phosphorus. Ammonia is also discharged in a wide variety of industrial and sewage effluents. In the present study 88.88 percent removal of free ammonia takes place from sewage water by Oscillatoria sp. There was an enormous increase of free ammonia (90.81%) by Scytonema sp.  The increase of free ammonia is due to the conversion of nitrogenous compounds from unavailable form to available form.. Lee and Lee et al., (2001) working with Chlorella kestrel reported that the higher removal of ammonium from wastewaters. Muthukumaran et al.,(2005) working with industrial effluent found Thalassiosira weissflogii to be better organism for removal of ammonium from wastewaters.

Nitrate content in the present study was increased to 60.00 percent when the sewage water was treated with Oscillatoria sp and 33.33 percent by Scytonema sp. Biological nitrogen removal of an effluent without substrate addition is possible if the effluent contains enough biodegradable organics to denitrify all its nitrifiable nitrogen content.  When sewage water is discharged to sensitive receiving water with low dilution, the nitrification process in wastewater treatment is encouraged to reduce effluent toxicity resulting from ammonia-N. In the aqueous environment, the effects of nitrate and nitrite are largely associated with increased algal and plant growth where nitrogen is the limiting nutrient.

In the present study the sewage water was treated with Oscillatoria sp and the chloride content was reduced to 48.65 percent and 61.74 percent by Scytonema sp. Similar observation attributing 30.00 percent chloride reduction under laboratory conditions by Halobacterium and only an additional 12 to 17 percent with cyanobacterium was reported in ossein factory effluent (Uma et al., 2002). Vijayakumar et al.(2005) reported 40 percent reduction of chloride in dye effluent, when treated with Oscillatoria sp. Kotteswari et al.,(2007) reported 25.98 percent reduction of chloride when the dairy effluent was treated with Spirulina platensis.

Fluoride content in the present study was increased to 3.44 percent when the sewage water was treated with Oscillatoria sp and reduced to 17.85 percent by Scytonema sp.  Fluoride also enters aquatic systems as a result of its addition to domestic water supplies and resulting in effluent discharge. Kotteswari et al.,(2007) reported 45.28 percent reduction of fluoride when the dairy effluent was treated with Spirulina platensis.

Phosphates showed a gradual decline.  Reduction of phosphate in sewage water and its uptake by micro algae has been reported by Mittal and Senegar (1989)^. The effluent was treated with Oscillatoria sp phosphate content was reduced to 73.14 and 84.00 percent when the sewage water was treated with Scytonema sp on the 15^th day. Tam and Wong (1990) have reported over 90 percent removal in total phosphorus within 10 days of algal cultivation.

Silica content was increased to 54.23 percent when the sewage water was treated with Oscillatoria sp and 66.30 percent by Scytonema sp. Kotteswari et al.,(2007) reported 80.77 percent reduction of silica when the dairy effluent was treated with Spirulina platensis.

The BOD level was reduced to 33.33 percent by Oscillatoria sp and 50.00 percent by Scytonema sp, similarly, the COD level was reduced to 33.33 percent by Oscillatoria sp and 38.55 percent by Scytonema sp.  It thus becomes evident that reduction in COD was less compared to reduction in BOD. Thus it is obvious that the degradation sought was through biological activity and not through a chemical agent. Kotteswari et al.,(2007) reported 47.14 percent of BOD and 24.69 percent COD reduction when the dairy effluent was treated with Spirulina platensis. Similarly, Veeralakshmi et al., (2005) reported 50.00 percent of BOD and 11.54 percent COD reduction when the petroleum effluent was treated with Oscillatoria sp.

Cyanobacteria have a potential to serve as agents for the engineered or intrinsic remediation of surface water in situ. Possibility of reprocessing and utilization of cyanobacterial biomass generated during remediation, by a variety of biotechnologies (Kerby and Rowell, 1992). It is also possible that further research may lead to the discovery of novel genetic systems and enzymes of biodegradation in cyanobacteria.

From this study it was clear that when the growth rate of cyanobacteria in sewage water increases, the rate of reduction of different pollutants also increased. It was clear that new bioremediation technologies can be better monitor and better control many types of societal wastes from fast emerging. However, there is little incentive to find and develop new tools. Education is important in achieving the widespread practices of prevention, recycling, and remediation for the purpose of improving the future environmental and quality of life. Through education, societal customs could change ways that could both reduce and recycle waste products and preserve out environment for future generations.

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