Aerobic Treatment of Sugar Mill Effluent with the Addition of Nutrients

this reason a research programme was undertaken The suitability of the activated sludge process using both laboratory and pilot scale equipment for the purification of sugar mill effluents was to determine whether the process could be used to investigated, both on the laboratory and on the produce a final effluent complying with the repilot scale. The process was found to be suitable quirements of the Water Act and to establish the provided additional nitrogen and phosphorus were operating conditions that would be required. added, and tentative design criteria for a full scale plant for a typical sugar mill are included. Laboratory experiments The aim of these experiments was to establish Introduction the permissible COD loading range and the Sugar mill effluent containing dunder water influence of load factor on effluent quality and has a high oxygen demand and be classified sludge settling characteristics, and also the effects as a Strong organic waste. For this reason some of addition of supplementary nitrogen and form of pre-treatment is required before the waste phosphorus on these factors. is discharged to a local river or stream if the requirements of Water Act No. 54 of 1956 are to be Materials met. Dunder water obtained from a local mill Mill effluents do not normally contain toxic three times a week was used for the study. Due to materials and pollute only in the sense that the the very wide variation in COD concentration high concentrations of soluble carbohydrates in that occurred between batches (1 000 18 000 mg the waste provide a substrate for rapid biological COD/ 1) a COD of 3 000 mg/ 1 was adopted as growth in the receiving water body with conan average value for experimental purposes, and sequent depletion of the dissolved oxygen due to dunder water supplies were adjusted to this value bacterial respiration. The problem, therefore, is to before use either by dilution with water or by reduce the concentration of oxidisable material in addition of stronger dunder water or sucrose the waste to a low level before discharge. Since solution. the waste primarily consists of organic compounds it should be amenable to biological degradation. Analytical Methods In the treatment of organic waste both The analyses for Chemical Oxygen Demand aerobic and anaerobic organisms can be (COD), Biochemical Oxygen Demand (BOD) and employed. With an anaerobic system dissolved Kjeldahl nitrogen were taken from Standard oxygen is not required for the organisms and the Methods 4, and for phosphorus and nitrogen from degradable carbon is converted to carbon dioxide A Manual of Sea Water Analysis 5 . The Sludge and methane as end products. In an aerobic Volume Index (SVI) was determined by settling system dissolved oxygen is required and the for 1 hour in a 100 ml cylinder and noting the gaseous end product is carbon dioxide only. sludge volume: the suspended solids concentration Use of anaerobic degradation, usually by was determined on the same sample and the SVI impoundment in lagoons, has been reported from expressed as millilitres of sludgelg dry weight. India2 and Puerto Rico3 and a similar system has been tried in Northern Natal. The results obtained Batch feed experiments with these systems indicate that although subResults and Discussion To obtain an stantial removals of oxygen demand can be obestimate of the optimum load factor and the tained the final effluents will not meet three of the effect, if any, of supplementary nutrient addition, requirements of the General Standard for batch feed tests using sludge pre-conditioned to effluents, viz. a COD not exceeding 75 mg/ 1, dunder water substrate were carried out in aerated suspended solids not exceeding 25 mg/ l and a glass vessels. Equal volumes of dunder water were dissolved oxygen content not less than 75% of the introduced to each vessel but extra nitrogen and air saturation value at the prevailing temperature, phosphorus in the form of urea and potassium unless some form of final aerobic "polishing" of dihydrogen phosphate was added to one vessel to the anaerobic effluent is provided. alter the C0D:N:P ratio from 100:0,2:0,05 for More recently work with aerobic activated dunder water alone to 100:4,2:0,8 in that with sludge treatment has been reported from nutrients added. Australia'. The experiments were mainly of the Samples were withdrawn from each vessel a t batch feed type, concerned with determining the time intervals and clarified for analysis. This COD removed per unit of power consumption but procedure was continued until the COD reached a the results indicated that the process would be minimum value and started to rise again due to capable of producing a high quality effluent. For autolysis of the sludge organisms. Proceedings o f The South African Sugar Technologists' Association-June 1972