World over a number of experiments and research on wastewater management is ongoingThere are many techniques which have been proven on laboratory & pilot trials. Some of them have also been adopted in actual field conditions. A few such technologies have been described below.
1) Anaerobic baffled reactor (ABR)
An Anaerobic Baffled Reactor consists of a watertight tank with baffles that separate the tank into several compartments. The waste water flows through the series of compartments but the connections between the compartments are such that there is an upward & downward movement of the passing liquid. This enables an enhanced contact between the fresh wastewater entering the reactor and the residual sludge, containing the microorganisms responsible for anaerobic digestion of the organic pollutants.
- An ABR consists of a settling chamber for removal of larger solids & impurities followed by a series of upflow chambers. Number of such chambers varies according to the volume & impurity of the waste water.
- HRT (Hydraulic Retention Time) is relatively short & ranges from 48 to 72 hrs.
- The connection between the chambers is either with vertical pipes or baffles.
- Accessibility to all chambers (through access ports) is necessary for maintenance.
- The tank should have vent pipes to allow for controlled release of odorous and potentially harmful gases.
- Check for water-tightness regularly and monitor scum and sludge levels
- Remove sludge every 1 to 3 years (preferably by vacuum truck or gulper to avoid that humans get in direct contact with sludge)
- Leave some active sludge in each compartment to maintain stable treatment process
2) Reed Bed System/Phytorid System
A reed bed is essentially a water tight chamber filled with gravel and planted with specialized plants from the group called macrophytes or reeds, and used to treat wastewater. Wastewater is passed through the root zone of the reeds where it undergoes treatment. Inlet and outlet pipes are positioned below the gravel surface, so that the water always remains below the gravel surface, thus excluding human exposure to the wastewater, mosquito breeding and unpleasant odours.
A Reed bed system comprises of following components
- A sedimentation tank.
- A reed bed consisting of:
- Filling media generally gravels.
- Selected indigenous wetland plants (phragmite species, Canna spesies etc)
- Inlet & Outlet pipes
- System effectively removes suspended solids organic matter, BOD and COD.
- After primary settling in the sedimentation tank, the breakdown of contaminants is achieved by the controlled seepage of wastewater through the root zone of the selected wetland plants.
- Oxygen diffuses from the atmosphere to the wastewater
- Anaerobic treatment at the lower levels of the bed
- Nutrient and phosphorus uptake by the plants
- Organic pollutants are broken down as a food source by microorganisms and the plants, while the other contaminants, such as metals are fixed in the humic acid in the soil or mineral substrates in which the plants are rooted.
- During this process suspended solids, BOD and COD are reduced to an acceptable level.
- The out-coming water can be safely utilized in agriculture.
Operation and Maintenance
- Periodical cleaning of settling chamber
- Harvesting of plants when grown excessively
- Cleaning of gravels if clogged
- Cleaning of inlet and outlet pipes