Decentralized sanitation 

Decentralized sanitation: considering operation and maintenance right from the design stage

When designing a wastewater treatment system, the engineer’s objective is to design a treatment facility that meets the expected purification performance for the design flows and loads. He or she must also ensure that the treatment system complies with the MELCCFP’s Guide to Studying Conventional Domestic Wastewater Treatment Technologies as well as with the technical information sheet issued by the Comité sur les technologies de traitement des eaux usées (CTTEU), where applicable. But what about the operation and maintenance of the treatment system at the design stage? Simple design elements can make equipment maintenance much easier later on.

Decentralized wastewater treatment facilities systematically feature underground tanks (grease traps, septic tanks, pumping stations, etc.). These facilities must be easily accessible to allow regular maintenance, such as sludge and scum pumping, pump servicing and pre-filter cleaning. It is therefore important that access covers are lightweight and easy to open, especially in winter. Fibreglass covers or hinged aluminum access hatches make access to equipment much easier. Access shafts should also always be slightly above ground level, to prevent debris (grass, stones, earth, etc.) from slipping into the closing mechanisms of the hatches or into the threaded holes of the screws and preventing the covers from closing properly.

Septic Tanks

Septic tanks can sometimes be as much as a meter deep, making access to components difficult. It’s a good idea to provide sufficiently large openings to improve accessibility and visibility of the tank’s inlet and outlet devices. As the pre-filter needs to be cleaned at regular intervals, it’s important to have a handle that’s long and sturdy enough to facilitate its removal without requiring a person to lean into the tank. Also, requiring additional pre-filter cartridges to be stored in the service building enables quick and easy maintenance by simply swapping cartridges when cleaning.

Pumping Stations

Pumping stations require a lot of work: preventive maintenance, service calls, repairs, etc. This means frequent visits by maintenance crews.

Ideally, the pumping station should be located where a service vehicle can be parked nearby to facilitate interventions, such as pump replacement. If possible, the control panel should be directly on the pumping station for annual calibrations and troubleshooting. Since access to the equipment constitutes entry into a confined space, it is important to provide a guide bar system for rapid pump removal, or at the very least, a plumbing system that can be dismantled quickly and easily, thus avoiding confined-space entry into the station. The float support must also be accessible to facilitate cleaning, as this equipment needs to be cleaned regularly, particularly for grease-laden wastewater (restaurant, snack bar, etc.).

A standard submersible pump of just 0.5 HP can easily weigh 50 lb (22.7 kg). A lifting system for pump removal is an attractive feature, as it reduces the risk of injury to the maintenance crew. When designing the system, it’s important to specify that a spare pump will need to be stored in the service building, especially for raw water pumps that are more prone to breakage.

Building Mechanics

When it comes to building mechanics, here’s a non-exhaustive list of the different items to consider in terms of maintenance during the design stage. It’s important to plan for equipment redundancy, spare parts (static mixer, UV lamps, etc.), bypass devices, isolation valves and a purge system for sensitive equipment. The latter enables equipment replacement or maintenance to be carried out without shutting down the system or causing damage.

Adequate building ventilation helps prevent corrosion, especially where blowers or compressors are used to remove heat generated by the equipment. For ultraviolet disinfection equipment, it is important to allow a minimum clearance in the service building for the replacement of lamps and quartz sheaths.

Conclusion

The items listed in this article are relatively simple to consider at the design stage. On the other hand, some of them can entail substantial costs for the client, and the designer’s duty is to explain the advantages and disadvantages of each item so that the client can make an informed decision. The important thing to remember is that these items can greatly facilitate the operation and maintenance of equipment and make them operational faster when a problem occurs.

References :

MELCCFP, Guide for the study of conventional wastewater treatment technologies for domestic origin, Guide for the Study of Conventional Domestic Wastewater Treatment Technologies (gouv.qc.ca) 

Jean-Sébastien Grenier, Eng., MBA
Team Leader – Wastewater and Drinking Water Treatment
GCM Enviro Synergies Inc.
[email protected]