Parameters affecting HS emissions removal and re-circulating water quality in a pilot-scale sequential biological treatment system at a wastewater lift station in Brownsville, Texas, USA

Abstract

In this study, a pilot-scale sequential biological treatment system combining a biotrickling filter and biofilter was used to optimize the removal of variable emission H2S loadings ranging from 30 to 120 g m−3 h−1at a wastewater lift station in Brownsville, Texas USA. The biotrickling filter recycle water pH remained between 2.0 to 3.0 during the four months of unit operation and the overall removal efficiency for H2S was >99%. The biotrickling filter removal efficiency was 70 ± 8%, with an elimination capacity of 10 to 80 g m−3 h−1 while the biofilter elimination capacity ranged from 10 to 40 g m−3 h−1. The sequential treatment system was operated initially at an Empty Bed Residence Time (EBRT) of 120 s (50 s for the biotrickling filter and 70 s for biofilter) for two months and then at an EBRT of 60 s (25 s for biotrickling filter and 35s for biofilter) for the remainder of the operating period; remarkably, there was only a slight decrease in removal efficiency at 60 s EBRT. In order to qualitatively evaluate the changes in recycle water quality in the system on the performance of the unit in precipitating sulfur species, the equilibrium chemical model, Visual MINTEQ was employed. The model predicted speciation results based on the feed water quality and sulfur loadings, and also forecast some iron-sulfur complexes which have potential to form some complex precipitates. This research demonstrated that low pH re-circulating water quality in the biological treatment of H2S was possible without compromising the high removal efficiency, and that an improved understanding of the recycle water chemistry of the trickling unit of a sequential treatment system could be useful in the overall optimization of the process.