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-and that it would be satisfactory if Sir Stanton Hicks were to submit a prepared statement. It was accordingly arranged that this should be done. The statement submitted has confirmed our opinion that his attendance was not necessary. It does not cover any new ground, and so far as it is concerned with the importance of soil conservation and the value of compost, as we have explained, these matters were not in dispute. So far as the statement deals with sewerage problems, we are unable to accept his opinions as -authoritative. Cultivation of Water Plants 44. (1) The Drainage League's proposals for the cultivation of water plants in sewage effluent which would be discharged into a lake to be constructed in the Manukau Harbour met with strong opposition. For reasons which we think it is necessary to .state only briefly, we are unable to recommend that they should be adopted. (2) It should be explained that the league appreciated that the proposals were novel and might prove to be impracticable, and it therefore made it clear that it was not asked that effect should be given to them unless after full investigations had been made it was demonstrated that they could safely be adopted. (3) It was claimed by the league that the cultivation of water plants would have two advantages. In the'first place, it was contended that if the plants were grown in sewage effluent they would extract valuable mineral salts having manurial value from the effluent which cannot otherwise be recovered. Secondly, it was claimed that when harvested the plants would have a material value in supplying the vegetable matter required for mixing with sewage sludge and garbage for composting purposes, particularly because they would contain the salts extracted from the effluent. (4) It was admitted that the practicability of extracting the salts has never been •demonstrated. It also appeared that in the treatment of sewage by the ordinary processes the larger proportion of the salts is recovered, leaving in the effluent only a small proportion, and that under the most favourable conditions it is unlikely that more than 12 per cent, would be recovered with the aid of water plants. In these circumstances we consider that the league failed to show that the growing of water plants in order to recover the mineral salts would be justified. (5) We consider also that it was not shown that the cultivation of water plants was justified as providing organic matter .for composting. Of the estimated daily summer-time harvest of 4,000 tons,.only 200 tons of dry matter would become available, and having regard to the high costs involved in obtaining this quantity, the scheme would appear to be uneconomic. (6) There were, however, even more serious objections to the proposals. Although Mr. Robinson claimed that in addition to water-hyacinths and cress there are a number ■of other water plants which are suitable for the purpose, most, if not all, of the evidence had reference to water-hyacinths and cress, and we will refer only to these plants. It should be observed that cress has its roots in soil and hyacmths in the water, and that if the former is grown the lake would have to be kept shallow, which would be a serious disadvantage. In fact, the practicability of growing cress for composting was not seriously pressed by the league, and we think it is clear that it would be unsuitable. Leaving out of consideration for the moment the objections to the growing of hyacinths which were made on the ground of the potential danger to health and the nuisance that might arise from the impounding in the locality proposed of a large mass of foul sewage and from the algal growths that would be encouraged to develop (which are matters that in themselves raise grave doubts) there was much evidence of great weight to support the Drainage Board's objection based on difficulties connected with the plant itself. Unless hyacinths grow profusely they would be of little use. If, however, they grew profusely there is a strong probability that they would become a pest, as has happened in other countries. It is unnecessary to traverse the evidence on this point in detail.

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