More info would be required, ...
Published by Andre Visser, Process Engineer at Water Engineering Consult
More info would be required, but I would say at COD's of 4000mg/l one should consider anaerobic pre-treatment. On the positive side sludge production as well as energy requirements will be considerably less following an anaerobic treatment step. On the negative side complexity and capital investment could be more. An evaluation of the total system would be the only way to get a good indication of the best route.