The Press SATURDAY, JULY 24, 1954. Sewage Disposal

Press, Volume XC, Issue 27410, 24 July 1954, Page 6

The Press SATURDAY, JULY 24, 1954. Sewage Disposal

The visit to Christchurch of the American drainage experts, Professor C. G. Hyde and Dr. D. Caldwell, seems to have been most valuable. Although they commended the sewer and pumping programme and the general ideas of the Drainage Board’s staff on sewage treatment, it is plain that their report will show how the treatment of sewage at Bromley can be quickly improved. They have promised to produce a plan, which should be put into effect within one or two years, to overcome the serious overloading of the present treatment system. This should reduce the pollution of the Estuary in a way evidently not contemplated by the chairman of the board (Mr E. H. S. Hamilton) in his statement at the beginning of the year that only primary treatment of sewage would be needed for the next 10 or 15 years. On a longer view, Professor Hyde and Dr. Caldwell have set at rest fears that the sewage farm was too small for the city’s needs and that it could not be economically extended. They are confident that, if the treatment methods they recommend are adopted, the farm will meet the requirements of a city of 500,000 persons, and even that the existing tanks can be adapted to an entirely new system. The broad lines of the recommendations are similar to those now accepted at Auckland. The crude sewage will be divided first into sludge and effluent. The sludge will be treated by heat (derived, almost free, from the methane gas in the sewage) to kill harmful bacteria, and then will be available as a useful fertiliser, though deficient in phosphates. The effluent will go to large ponds (covering some 400 acres in the Christchurch scheme), where it will be purified by the oxygen in the air. The final discharge will be of a purity contrasting sharply with the pollution now flowing into the Estuary. In their report at Auckland the overseas consultants said there was no reason why the treatment area should not be laid out as. park. Though something along the lines of these recommendations appears to have been in the mind of the Christchurch Drainage Board, in the four years since the return of the engineer (Mr E. F. Scott) from his overseas visit, little progress has been made towards overcoming conditions that the Americans say should be remedied in one or two years. The board has been content to deliver more and more sewage to a treatment station that it admitted was inadequate. There has been some expert criticism of the overseas consultants’ new plans for Auckland on the ground of cost, which some engineers think they have underestimated. Whatever the merit of this criticism, it is based on considerations that do not apply in Christchurch. Here, no question occurs of the construction of miles

of new sewers; little storm water enters the sewers; and the climate is much drier, with little more than half the Auckland rainfall. In these conditions, recommendation of a method of treatment was much simpler at Christchurch; and there is every reason to hope that the advice of Professor Hyde and Dr. Caldwell will remedy one of the major weaknesses in the Drainage Board’s planning.