Nutrient addition to enhance biological treatment of greywater

This study compares the chemical oxygen demand (COD) removal and respiratio n rates of a microbial population treating real and synthetic greywaters do sed with nutrient supplements. The nutrient composition of the real and syn thetic greywaters was analysed and the dosing regime for nitrogen, phosphor us and a range of trace metals planned accordingly. The doses consisted of eight single additives (macronutrients and trace metals) to the control gre ywater and six trace metal additions to C:N:P balanced greywater. The COD r emoval for the control real and synthetic greywater in lab-scale activated sludge systems (0.038 and 0.286 kg COD kg MLSS-1 d(-1). respectively) confi rmed nutrient limitation and the poor degree of greywater treatment. Nutrie nt dosing increased the COD removal rate and oxygen uptake rate in many cas es. The greatest stimulation of microbial activity was observed with zinc a dditions lo C:N:P balanced real greywater (1.291 kg COD kg MLSS-1 d(-1) ove r 30 times the control). Inhibitory effects to various extents were rare an d limited mainly to the additions of metals to synthetic greywater. The dom inance of chemicals effects was observed on addition of some micronutrients : notably iron and aluminium, metals on which many coagulants for use in bi otreatment of other wastewaters are based. The data indicate that the impac t of understanding microbial processes and the nutrients required For waste water treatment can only serve to optimise process efficiency for the propo sed treatment of greywater. (C) 2001 Elsevier Science Ltd. All rights reser ved.