New loan will keep work going

Press, 23 February 1977, Page 10

New loan will keep work going

With two years and a half of work behind them on extensions and modifications to the Bromley sewage treatment plant, the Christchurch Drainage Baord’s engineering consultants, staff and contractors are moving into the second half of the job, the board having Local Authorities’ Loans Baord approval to raise an additional 52.9 M to enable the work to proceed. At present the board’s contractors are adding the finishing touches to a new sludge digester tank which is about 10m deep and 27m in diameter and has a capacity at about 4M litres.

In recent weeks, some young Christchurch engineers, who are also expert skin divers, have been combining professional and leisure-time skills to obtain information about the nature and directions of currents in the digester, which has been filled with water for the data-finding programme. The digester will be commissioned shortly. On another part of the Bromely site, work has started on the construction of the second plastic media-filled trickling filter tower, which should be commissioned in about

eight months. The first tower was commissioned at the end of December and is coping with the entire Bromley sewage load. But, from the man-in-the-street’s viewpoint, the most interesting project for the future at Bromley is incorporation within the plant of a power generating plant, the fuel for which will be the methane gas, which is produced from the process of heated sludge digestion. Commonly called sludge gas, it has a high calorific value and it will

be valuable fuel for driv* ing engines which will be coupled to alternating generators. By using the gas in this manner, it will be possible to generate about 75 per cent of Bromley’s peak power requirements. It was estimated last May that this method of power generation would save the board up to $150,000 a year in power charges. Now, with higher charges in the offing, the savings will be even greater. But, on top of the power-saving advantages

of this system, there is another cost-saving advantage. The heat generated by the gas-driven engines will be used to heat the sludge digesters, which means that Bromley’s fuel oil demand will diminish. The over-all efficiency of using sludge gas in this manner has been estimated at about 66 per cent and, when measured in terms of the cost of imported fuel oil, that represents an annual saving in fuel costs alone of about $500,000 on the basis of present fuel oil costs.