Constructed wetlands lie in-between lagoons (4.2.3) and land based treatment systems (4.2.4). They are based on natural wetlands, which act as a water filter and purifier. A constructed wetland consists of a gravel bed in which wetland species, such as reeds, are planted (Figure 23). Wastewater, usually after the settling of solids, passes through the gravel bed. The flow of wastewater can either be surface or sub-surface. The bacteria that are attached to the surfaces of the bed and plant roots degrade organic substances. The reed beds remove N and P as or more effectively than conventional wastewater treatment plants. They are suitable for treating domestic sewage as well as other forms of wastewater such as contaminated groundwater and agricultural and animal waste. Wetland plants take up nutrients (nitrogen and phosphorus) when water residence time is long. Long-term nutrient removal requires harvesting of the plants. Constructed wetlands need to be designed to minimise problems with insects (mosquitoes and midges).
The wastewater generated often is concentrated with high proportions of nutrients (CNP) and other mineral ions. In the developing countries there is a growing consensus on the enormity of wastewater generation and at the same time the technologies available to treat the same becomes highly expensive with chemical based systems10,11. The N and P concentrations of municipal wastewaters in the urban areas of India like Bangalore ranges from 90-30 and 10-33 ppm respectively10. Algae being the most rapid assimilators of nutrients effectively grow in these nutrient rich environment makes them the most suitable candidate for low-cost wastewater treatment28. Efforts show energy generation from algal biofuel with environmental and economic sustainability4,19,21, 27.
Wastewater treatment high rate algal ponds for biofuel production
Water samples collected from wastewater pond were rich in nutrients. Euglena species were abundant in wastewater with Amm.-N level of 20 mg/l with higher BOD and COD values of 224 and 362 respectively out of which 50 % i.e. 115 mg/l was only algal BOD (Table 1). These species contributed to higher TSS load of 389-465 mg/l. The TKN values were 44 mg/l with a very minimal nitrification occurring with, nitrate and nitrite values of 0.18 and 0.01 mg/l respectively. It was observed that Euglena sp. were responsible for BOD removal of ~60%, TSS removal of 80% and Amm-N removal of 35%. The wastewater of the treatment ponds showed an algal count of 4.78 X 105 cells/ml. Higher algal cell densities were found on the top 40 cm layer of the treatment plant. Earlier studies have been performed on Scenedesmus sp., Botrycoccus sp., Chlorella sp., Chlamydomonas sp., Micracitinium sp. etc. from primary or secondary treated municipal wastewaters for their lipid content (Table 2).
> Diatom Algae – Sewage Treatment >
The process of photosynthesis is illustrated by the equation :
The overall effect of this reaction is to produce new plant life, thereby increasing the number of algae.
Wastewater treatment by algal turf scrubbing
Although the reactor itself has a simple configuration with no moving parts, pumping of the feed is still required. Methane gas is produced which needs special handling procedures to prevent leakage and explosion. Wastewater treated anaerobically requires further aerobic treatment to reduce its BOD and odour. Excess granules need to be treated prior to reuse or disposal, although currently there is a demand for the granules to start up UASB reactors. The mixture of methane and carbon dioxide (termed 'biogas') can be combusted and used for heating the content of the anaerobic reactor or for other purposes.
Natural Systems for Wastewater Treatment in Cold …
In the Upflow Anaerobic Sludge Blanket (UASB) process settled wastewater is passed upward through a sludge blanket. The sludge blanket consists of anaerobic bacteria, which have developed into granules. Because of the high settling velocity of the granules, the granules are not carried over in the upflowing wastewater. A high concentration of bacteria is therefore retained in the tank. The tank itself has no internal moving parts (Figure 25). If wastewater is distributed evenly at the base of the tank, mixing between the wastewater and the granules of bacteria is promoted by the carbon dioxide and methane gases produced by the anaerobic treatment process and the upward moving flow of the wastewater.
refers to wastewater treatment systems which ..
Blooms of Spirogyra species were observed in the shallow waters at a comparatively lower level of Amm-N (9.54 mg/l) in the wastewater fed Varthur lake (Table 1). BOD and COD of the region were moderately high (Table 1). Dissolved oxygen levels of ~18 mg/l (Mid-day) were higher due to algal photosynthesis with reasonably high phosphate levels (Table 1). Phormidium species were prevalent as floating masses and to a smaller extent attached to the substratum near the outlets of Varthur lake in a highly reducing environment having an ORP of -214 mV with a slightly higher BOD, COD and lower Amm-N values (Table 1).