Water ways

Sudhir Kumar, engineering group manager at MWH.
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Wastewater – stay big, go small?
Given the cost of transmission systems, and the fact that human settlement in the Middle East can be sparse and intermittent, there have been calls for a greater decentralisation of wastewater plants.

This would entail both a scaling down of wastewater processing plants and of water transmission networks.

Both options have their cost advantages. Large, centralised plants are low in production cost, yet high in transmission cost, while the opposite is true for decentralised plants.

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As the experts point out, a decision on the size of the plant should be taken on the basis of every individual case.

“There is no fit for all solutions and each case should be techno-economically evaluated considering key factors such as project catchments, topography, total demand, ground condition and other design requirements,” says Kumar.

But centralisation is the better option in most cases, thinks Zambubi: “Plants are expensive to build and operate, typically you have relatively few wastewater plants because they are expensive pieces of kit to put together. So its still cheaper to have quite a lot of pumping than to have a lot of wastewater plants.”

Zambuni points also to the increasing trend towards green solutions, which is evident especially in power generation, where decentralised small-scale plants contribute to electricity production.

Likewise, ecologically friendly wastewater treatment plants are starting to come to the market.

He feels that the time is not right for those solutions from a cost perspective: “Water is different from other utilities, such as distributed power generation through biomass, for instance. With wastewater, the economics point to larger plants in smaller numbers still.”