I N S P I R A T I O N : Concepts

Proposal for Setting up of Anaerobic Waste Water Treatment with Pressure Filtration for treatment and recycling of Effluent from Comfort Station at Chottanikkara Temple, Ernakulam

Description of project
As understood, the Comfort Station has toilet and bathing facilities for the piligrims visiting the temple. During peak Sabarimala pilgrimage time of January / February, the waste water generated goes as high as 1,50,000 liters per day. Presently, the comfort station building is poorly designed and built with very little ventilation and natural lighting. The building ideally needs to be redone with better finishes and detailing.

The effluent from the toilets and bath areas are led to a septic tank after which the liquid effluents are allowed to percolate to the soil. But since the water usage is very high, the percolation is very ineffective and semi treated effluent flows partly on surface creating unhygienic conditions and hardships to the local populace.

The Devaswom wishes to set up an effective treatment system for the toilet waste. The suggested DEWATS (Decentralized Waste Water Treatment System for the project is as follows

Primary treatment
Primary/ Pre-treatment is used as a screening and sedimentation process, separating the liquid part of the waste from the solid matter. A device called a Settler is used for this phase. Within the settler, two main treatment processes take place. First, a mechanical treatment retains contaminants by sedimentation/ floatation and the waste water from the clarified layer flows through the outlet. Second, through biological treatment, the remaining organic pollutants are partly decomposed by micro-organisms. Through the digestion process the accumulated sludge is stabilized. Storage volume for sludge is provided for 12 months desludging interval. Average reduction of BOD in the settler is expected to be between 20 and 25%.

Typical Section of a Settler

Secondary treatment
In secondary treatment, biological and natural chemical processes are used to digest and remove most of the organic matter.

Typical section of the Baffled Reactor

A device called Baffled Tank Reactor (ABR) is used for this phase. Several up flow chambers are constructed in series to help digest difficult degradable substances. The sewage flow is directed from top to bottom and up again. During the process the fresh influent is mixed and inoculated for digestion with the active blanket deposit of suspended particles and microorganisms occurring naturally at the bottom (activated sludge) of each chamber in such conditions.

The BOD reduction rate of the baffled reactor is about 75 –85%. The pathogen reduction is in the range of 40 – 75%. The Baffled Reactor is resistant to shock load and variable inflow, the operation and maintenance is simple.

Anaerobic Filters: The Anaerobic Filters are fixed bed reactors. The process applies anaerobic organisms for degradation of waste water pollutants. The design is based on continuous upstream flow process. Filter media helps increase surface area for active bacteria. Reduction of BOD is about 70%. The Anaerobic Filter can be integrated with the Baffled Reactor.

It is expected that after the above treatment, the treated waste water shall have a BOD value of less than 50mg/l.

Horizontal Planted Gravel Filter : The Horizontal Planted Gravel Filter (also called Root Zone System) acts through the combined working of the filter material, the plants and the roots in the device. The Horizontal planted gravel filter is made of reed planted filter bodies consisting of graded gravel. The normal depth is 50- 60cm. The main removal mechanisms are biological conversion, physical filtration and chemical adsorption. Mechanisms of BOD removal are mainly aerobic and anoxic.

Polishing Pond
The treated sewage becomes “living water again” by undergoing further biological treatment, through natural UV exposure and flowing through an open water body, a Polishing Pond, with all the necessary natural elements such as fish, frogs, dragonflies and different aquatic plants. At this stage the recycled wastewater can be reused without posing any treat to human handling.

Typical section of Polishing Pond

Design Details
Considering the space availability, usage pattern etc, it is suggested that the Settler and Anaerobic Baffled Reactor with Anaerobic Filters are provided for an effluent discharge of maximum 150000 liters per day.

The expected BOD of the effluent after this is expected to be around 30mg/l.

After this, 30,000 (thirty thousand) liters of the treated effluent water shall be let through a Horizontal Flow Planted Gravel Filter. This shall help further treat the water to a BOD of 20mg/ l. After this the treated water is to be collected in a polishing pond for natural UV treatment. The water from the polishing pond shall be let through a pressure filter and disinfected with chlorination after which this water shall be ready for reuse for flushing in the toilets.

At an average of 10 liters per flush, there shall be enough water for 3000 flushes per day.

The rest of the 120000 liters of water are to be let through planted drains with vetiver planted. The vetiver shall help to further treat the water and allow better percolation too. The vetiver can be planted along the slope in hedgerows and along the present drain.