Decentralized Sewerage ...

Decentralized Sewerage Collection and Treatment

Unfortunately, while seeming straightforward, the issue of putting sewage collection and treatment solution into villages, towns and smaller cities is difficult for two reasons:

1. Organic unplanned urban growth
2. Unreliable, Low or Variable water supply often below hydraulic cleansing velocity

Conventional sewer networks are designed to be built in areas where there are neat straight roads and cannot therefore be easily placed in areas with short or curving roads. In addition; the low and often seasonally variable water supply means that conventional sewers cannot effectively transport sewage without the solid component falling out of suspension, choking the pipe network and increasing maintenance costs. This problem can often only be rectified by increasing the slope of the pipes which then results in pipes having greater depths and deeper manholes which increase the risks and costs associated with maintenance as additional water is not available. Combined this with the additional risk to lives caused by houses collapsing as deep trenches are dug in narrow lanes and one begins to understand why open drains, septic tanks and soak pits are employed to convey wastewater away.

Full disclosure: I run the India operations of Clearford Water Systems Inc., (www.clearford.com) a Canadian company specializing in just such solutions and the below is our solution.

The Clearford One system removes sewage solids at source in ClearDigest™ Smart Digesters™ before releasing liquid effluent into the SBS® ClearConvey™, a network of smaller diameter pipes that carries liquid sewage to an optimized Waste Water Treatment Plant (WWTP) facility for final processing.  The reduced contaminants present in the liquid effluent allows for more efficient recovery of reusable water using the ClearRecover™ WWTP package.  Recovered water can be safely returned to the environment or redistributed for non-potable uses such as toilet water, fire protection, irrigation, and groundwater recharge. 

ClearDigest™ Smart Digester™ tanks provide decentralised pre-treatment of the organic component of wastewater through anaerobic digestion, while retaining inert solids in the tank.  These Smart Digesters™ greatly reduce the solids and organic loading in the liquid effluent while continuously decomposing sewage solids.  Clearford patented technologies enhance the natural processes in the tank such that they are pumped out only after decades of normal use.  Peak flow is also reduced, resulting in a consistent trickle of wastewater to the SBS® ClearConvey™ collection network. This process does not use cultured bacteria, chemicals or electricity to operate.

ClearConvey™ Small Bore Sewers® (SBS®) use modern HDPE piping technologies to achieve a watertight network of small diameter pipes for the collection and conveyance of the liquid effluent by gravity.  The flexibility of small diameter pipes allows for adaptable installations in shallow trenches with less material requirements.  Additionally, the seamless fusion of pipe sections eliminates infiltration to the system and stops leakage of sewage to the environment.  Thus, ClearConvey™ overcomes many of the constraints associated with conventional sewer systems. The network also eliminates the need for manholes which are the source of the majority of inert solids found at WWTP bar screens from entering pipe networks.

At the end of the system treatment requirements are significantly reduced compared to conventional systems, as solids and organic matter are reduced by a typical 65-75% in terms of BOD, COD and TSS loads in the liquid effluent reaching the WWTP facility, and peak flows are reduced to a factor of 2x.  This allows for the water to be treated and recycled at significantly lower O&M costs.