Belfast Sewage May Need Own Plant

Press, Volume CI, Issue 29801, 18 April 1962, Page 17

Belfast Sewage May Need Own Plant

Sewage treatment facilities at Belfast would be more flexible than the provision of new trunk sewers to carry wastes to the new purification works at Bromley, the sewage treatment engineer (Mr D. L Steveni said in a preliminary report to the Christchurch Drainage Board last evening. Preliminary investigations were concerned with two alternative means of disposal —the provision of new trunk sewers capable of carrying any possible future wastes, both domestic and industrial, from Belfast to Bromley; and the provision of separate treatment facilities in the Belfast area to produce an effluent of a standard that would maintain the standards which would no doubt be formally promulgated for the Waimakariri river in the near future, Mr Steven said. The estimated flow at present was approximately 2.5 m gallons a day, of which 95 per cent, was industrial. Providing residential development did not extend very far beyond the limits envisaged by current town-planning schemes, the domestic flow would always represent only a small proportion of the load. Early Treatment Industrial wastes from Belfast were of extremely high strength and biochemically i nstable, and if at all possible should receive treatment at an early stage rather than after a long period in transit. The lower velocities which would result from the construction of a trunk sewer with provision for higher future flows would materially : fleet the control of the treatment processes at Bromley, and conversely the provision of more limited capacity and consequent higher velocities could bring about the necessity for costly duplication of tn- eight miles of trunk sewer. The pollution load from the Belfast area was approximately that of the domestic load from Christchurch at present. Such an additional load would require extensions to the plant greatly in excess of those at present envisaged The present development of the metropolitan area indicated that there would be few, if any. major contributing areas along the probable line of a new sewer. Discharge to River "At the present time the relatively untreated wastes discharge into the south branch of the Waimakariri river, and during the summer season pollution of the recreation areas adjacent to the road bridge is regarded bv the health authorities as serious.” Mr Steven con-t-nued. Future treatment must result in a significant reduction of all forms of pollution—visible, biochemical, and bacteriological. The visible pollution and heavy oxygen demand can be reduced by the us of the anaerobic aiges-

tian process, and bacteriological contamination may be reduced by making the most effective use of dilution or by treatment in oxidation ponds, or both.” Anaerobic digestion proceeded most economically and effectively at relatively high temperatures—Bo to 95 der*es Fahrenheit although

effective digestion could proceed with lower temperatures of 75 to 80 degrees. Waste waters from the freezing works were discharged at much lower temperatures—ss to 60 degrees—with a consequent heavy demand for digester heating.

Some separation might be necessary so that the more concentrated wastes discharged could be subjected to anaerobic digestion, the subsequent effluent being treated together with the weaker industrial wastes and domestic sewage by more conventional methods.

The seasonal nature of the v irk at Belfast was a complicating factor. No conclusions should be drawn for his comments. Mr Steven said. They related only to facets of the problem immediately obvious. and were brought to the board’s attention solely to illustrate the extent of the problem and the scope of the investigation. Only a proportion of the pollution came from the board's own area, commented the chairman (Mr F. R. Price). He said Mr Steven would give a definite report by June.