Performance of variable climate waste stabilisation pond systems during the critical spring warm-up period

Whalley, Caroline (2008) Performance of variable climate waste stabilisation pond systems during the critical spring warm-up period. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The research investigated some of the factors influencing the rate of stabilisation of wastewater in the spring period in variable climate waste stabilisation ponds (WSP): in particular, the potential for bringing forward the discharge date by optimising storage capacity and dilution. Experiments consisted of batch-fed systems under both controlled and natural conditions at the University of Southampton, UK; semi-continuous fed units in Almaty, Kazakhstan; and a trial WSP at Lockerley, Hampshire, UK. Batch-fed experiments revealed a three-fold reduction in BOD load produced a three-fold increase in overall BOD removal rate. Significance of dilution in improving overall removal rates with changing COD concentration increased when light availability was reduced as the photosynthetic process was adversely affected at higher initial loads. The onset of an algal bloom and recovery to net oxygen production were delayed by up to 16 days with the increase in COD, leading to odorous conditions for longer. Semi-continuous fed 780-1 tanks were operated as maturation ponds with storage dates from 1 December-l May and 1 January-l June. Both appeared to reach summer steady state COD values of 25-40 mg rl well before their nominal discharge dates, with little difference between them. Five tanks were operated at HRT of 15-60 days and surface loading rates of 33-133 kg BOD ha- 1 d- 1 . No long-term adverse effects of reducing the HRT were shown though delays of 4-6 weeks in the rise in both COD and nutrient removal efficiency were apparent in the range 15-20 days. Separate dilution experiments in 25-1 units which included a period of ice cover supported findings of the 780-1 tanks whereby an earlier improvement in removal efficiency is possible when the starting load is reduced. Differences observed in the bucket experiments that experienced a period of ice cover and those conducted under a period of 'open water' suggest improvement possibilities through the dilution of the winter load. Lockerley pond system demonstrated for seasonal communities could provide a cost-effective and reliable alternative to wastewater treatment in a UK climate. Both modes of operation were reasonably successful; the long retention time in Phase 1 produced suitable effluent quality by November; in Phase 2, BOD and suspended solids were able to meet discharge requirements throughout summer but further treatment is required for nutrients to meet discharge standards. intermittent discharge that Results indicated that there may be scope for alternative operating protocols designed to maximise performance and economic potential of variable climate pond systems \vith respect to making wastewater available early in the spring.

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