Municipal contracts

Case studies

1. A contractor refurbishing a series of pressure filters was having difficulty obtaining a good air scour pattern test. An investigation showed a design flaw in the laterals. A redesign of the laterals was required. The problem was exacerbated by the limitations of the original equipment and a novel solution was found which managed to utilise a lot of the faulty installed underdrains. The completed design and modifications to the filter collection channels was very successful giving a 100 % air scour distribution pattern.

2. An assessment of membrane treatment plants was made for a Water Company and assistance was given in the formulation of the specification , testing and validation of the proposed plants.

3. Assistance was given in the hydraulic calculations and preparation of proposal documents for a water contractor for two municipal treatment plants.

4. A major water works had installed a completely new chemical handling facility and was experiencing severe difficulties with the lime batching system. The lime was batched into a small hopper under load cell control and then blown into lime slurry tanks for mixing with water. The lime slurry was then recirculated through a ring main serving the various dosing pumps. The first problem was with variable weight measurement of the hopper. This was found to be due to inadequate venting causing a small pressure increase on the load cells. This was easily resolved. A second problem was found with the level sensors in the lime slurry tanks caused by lime dust. This was solved by installing a vented shroud around the probes. The final problem was in the changeover between lime slurry tanks at low level. Examination of the system showed cavitation just starting in the pumps before low level was reached. This was sufficient to airlock the pump during the changeover and the pump would fail on the new tank. The NPSH requirement for the pump flowrate was too high and by adding a flow restriction in the ring main the NPSH was reduced and the cavitation stopped.

5. A Middle East government water standards regulator was investigating a new Reverse Osmosis desalination plant to be built to feed into the existing water distribution system. The existing water plants were all multi stage distillation plants and consideration needed to be given to the water quality specification for the new plant.
Major additional capital expenditure would be required if the specification of the W.H.O was to be implemented as a two stage rather than a single stage desalination plant would be required. An investigation into water use and blending was carried out and also an evaluation of the key problem parameters such as Boron was completed. A report was presented to the government organisation so that a water quality specification could be imposed on the successful contractor