Board May Ban Some Waste-disposal Units

Press, Volume CIV, Issue 30761, 27 May 1965, Page 13

Board May Ban Some Waste-disposal Units

A definite policy on wastedisposal machines, with prohibition of some commercial units, was proposed by Mr P. J. McWilliam, the chief engineer, in his report to the Christchurch Drainage Board. He said it was becoming clear that their use could create problems for the board. In Christchurch, with the flat grades of many sewers and consequent low velocities, there was a risk of the ground-up solids settling in the pipelines, said Mr McWilliam, listing the difficulties. Blockages and additional cleaning could result. Some trouble had already occurred with commercial units. Commercial units could be used for the disposal of solids that would otherwise not be disposed of in sewers. A quantity of water had to be used to carry the ground-up material into the sewer. This increased the water the pumping stations had to handle. Fat From Food Where food was prepared, units could reduce the effectiveness of grease traps, as a lot of finely-ground fat could be washed through the trap and into the sewer reducing its capacity and blocking it eventually. At the treatment works the quantity of sludge to be handled would be increased. This was not a problem at present, but when the plant approached the design loading, additional digester capacity would be required. “While it is appreciated that the sewerage system may be looked upon as a rubbishdisposal system, it does seem wrong that solids are ground up, washed into the sewer, and then have to be recovered for treatment at the treatment works to ensure that the receiving waters are

not polluted,” Mr McWilliam said.

He proposed that the installation of the small kit-chen-sink type of unit in onefamily dwelling units should continue to be allowed. The installation of commercial units should be permitted in foodmarkets provided the conditions of the receiving sewer were adequate to handle the discharge, which should be treated as a trade waste and charged for. A foodmarket should be defined as a place retailing unprocessed, perishable food. Other commercial units, Mr McWilliam suggested, should be prohibited because of the difficulties and costs that could be associated with them. The board referred his report to the trade wastes committee.