Adaptation of the CAS test system and synthetic sewage for biological nutrient removal - Part II: Design and validation of test units

A global increase in biological nutrient removal (BNR) applications in wast ewater treatment and concern for potential effects of anthropogenic substan ces on BNR processes resulted in the adaptation of the Continuous Activated Sludge (CAS) laboratory test system (cf. guideline OECD 303A [1] or ISO 11 733 [2]). In this paper two novel systems are compared to the standard CAS unit: the Behrotest KLD4(R) and a University of Cape Town system (CAS-UCT). Both are 'single sludge' systems with an anoxic/aerobic and an anaerobic/a noxic/aerobic configuration, respectively. They both can simulate the essen tial processes of full-scale BNR installations. The units where fed with a specially designed synthetic sewage, Syntho (cf. Part I of this study), or its precursor BSR3 medium. The performance of the two new units was benchma rked against the standard CAS system in terms of carbon/nitrogen/phosphorus (C/N/P) removal, as well as primary biodegradation of the surfactants line ar alkylbenzene sulfonate (LAS) and glucose amide (GA). Both systems allow to easily achieve stable excess N- and P-removal. Experi mental C/N/P removal data compared closely with simulations obtained with t he IAWQ Activated Sludge Model No. 2 (ASM2), and with full scale BNR plants with a similar configuration. In both units the effluent concentrations of the surfactants tested were si gnificantly reduced in comparison to the standard CAS system (up to 50% les s). No adverse effects on BNR were noted for the test surfactants dosed at 400 mu g/l together with an overall surfactant background concentration in the feed of ca. 20 mg/l. The proposed systems hold potential to complement the standard CAS system for situations where advanced sewage treatment plan ts with BNR need to be simulated in the laboratory with minimum effort. (C) 1998 Elsevier Science Ltd. All rights reserved.