Studies on the breakdown of irrigated food processing wastes by soil micro-organisms: a thesis submitted in partial fulfilment of the requirements for the degree of Master of Agricultural Science in the University of Canterbury, Lincoln College

Abstract

'Nature's Sewer' is a term which has often been applied to the soil, in the sense that the great variety of micro-organisms residing in the soil ensures that, in almost all instances, materials introduced into it will be readily broken down. Until the advent of industry, the concentration of bi-products discharged on to the soil at any one time was relatively low, the composition of these wastes being in forms easily assimilated. Wastes produced nowadays by industry are often found to be in a form which is not readily broken down. Amounts and concentrations of wastes far in excess of the wastes from natural systems are often produced.

Biological systems, including the soil, are reasonably adaptable to changes in their environment. Time is needed however for this adaptation, and there are limits to a system's ability to change. Due to the balance maintained within biological systems, with energy inputs equalling outputs, "overloading" does not often occur to the detriment of the system. This equilibrium can, however be unbalanced by an artificial input.

The present investigation at J. Wattie Canneries, Hornby was initiated to determine the effect of food processing wastes, irrigated by the border dyke method, on to specially prepared land.

During the summer months, November-March, peas, broccoli, asparagus and brussel sprouts are the main vegetable crops processed. Jams from apricots, raspberries, strawberries and black currants are also made during the summer. In the winter one of the main vegetable crops processed is potatoes for the production of chips called "French Fries".

The potato chip production involved the heating of the potatoes in a rotary steam peeler at 90 p.s.i. for approximately 45 seconds, chipping the potatoes with a crinkle-cut chipper, blanching the chips at 88°C for four to six minutes, frying for one minute in fat (Chefade) at 191°C and freezing the chips at -18°C to -20°C before final bagging.