The full cost of a sewage treatment plant

Separate purchase, installation and ownership

The plant price is only one line. A complete proposal may include design, excavation, base, inlet and outlet work, covers, ventilation, electrics, control panel, alarm, pumps, commissioning, approvals, waste removal and reinstatement. The site's levels and discharge route can change the scope substantially.

Then add ongoing electricity, maker-specified servicing, desludging, consumables and eventual replacement of powered or mechanical parts. Ask for these as assumptions, not promises.

Build one comparison table

For every quote, record:

• exact make, model and design population;
• certified performance claimed and the document supporting it;
• proposed inlet, outlet and discharge route;
• gravity or pumped sections and the reason for each pump;
• electrical supply, protection, alarm and isolation scope;
• commissioning and operator handover;
• service frequency, likely service scope and warranty conditions;
• desludging guidance from the maker;
• parts excluded from warranty; and
• groundwork, waste, approvals and reinstatement exclusions.

If one contractor has priced a gravity outlet and another a pumped outlet, they are not the same proposal.

Estimate electricity from the proposed equipment

Ask for rated power, operating pattern and any intermittent components. A simple estimate uses power in kilowatts multiplied by expected running hours and your tariff, but real use depends on the equipment and loading. Do not borrow a consumption figure from another model.

Treat an air blower, pump, control unit and alarm separately. Ask what continues during a power cut and follow the maker's restart instructions. See the power-cut plan.

Price the discharge, not only the treatment

A treatment plant does not create a lawful outlet by itself. The discharge may need a drainage field, pipework to an acceptable flowing watercourse or another designed route, with the applicable regulator conditions and permissions. Ask which part of the quote demonstrates that the proposed outlet is suitable.

Ask for a ten-year ownership schedule

This need not predict prices. It should list expected annual or periodic actions: service visits, desludging, electrical checks, maker-specified parts and record keeping. Apply your own current prices and contingency. The value is seeing obligations that a low equipment quote leaves outside the first invoice.