Microbial Dynamics and Bioreactor Stability in an Oil-Absorber-Bioscrubber System Exposed to an Alternating Sequence of 1,2-Dichloroethane and Fluorobenzene

Michalis Koutinas1, Ines Baptista1, Andrea Meniconi2, Ludmila G. Peeva1, Paula ML Castro3, and Andrew G. Livingston1. (1) Department of Chemical Engineering and Chemical Technology, Imperial College London, Prince Consort Road, SW7 2AZ, London, United Kingdom, (2) Dipartimento di Ingegneria Chimica, Mineraria e delle Tecnologie Ambientali, Universita Degli Studi di Bologna, Viale Risorgimento, 2, Bologna, 40136, Italy, (3) Escola Superior de Biotecnologia, Universidade Catolica Portuguesa, R. Dr. Antonio Bernardino de Almeida, 4200-072, Porto, Portugal

A critical characteristic of industrial waste streams, when biological treatment technologies are applied for the removal of inhibitory pollutants, is the random variations in the pollutants concentration profiles. Although past studies have extensively described the responses of biological systems to changes in pollutant concentration, there has been limited work investigating their response during periodical switches in carbon source [1]. This extreme scenario, usually produced from a sequence of batch processes, is reported in the literature as “sequentially alternating pollutants” (SAP), and describes the case when the pollutant composition is alternating sequentially from one set of compounds to another over cycle periods of days or weeks. Therefore, if the microorganisms used in the process are specific for a single pollutant, re-acclimation periods might be needed when the specific pollutant is re-introduced to the process after a long period of non-supply. The above suggest the need for development of a robust technology to control the negative effects of SAP in biological systems.

The aim of this study was to investigate the potential for an oil-absorber placed upstream to a bioscrubber configuration to act as buffer for sequentially alternating loads of 1,2-dichloroethane (DCE) and fluorobenzene (FB) in waste gas streams.

A bioscrubber system (without the oil-absorber present) was inoculated with strain F11 and Xanthobacter autotrophicus strain GJ10 and was submitted to sequential alternations of the pollutant fed (DCE and FB). The re-introduction of the substrates after each cycle caused system instability as indicated by the evolution of the effluent gas and biomedium DCE and FB concentrations, carbon dioxide production and total organic DCE and FB discharged.

An oil-absorber, utilising a cost effective and environmentally friendly absorbent (Sunflower Oil), was introduced prior to the bioscrubber in order to control the negative effects caused by the sequential switches in the feed composition between DCE and FB. The performance of the combined Oil-Absorber-Bioscubber system was stable after the substrates re-introduction following each switch in the feed, as indicated by the substantial reduction in the effluent DCE and FB concentrations, stable carbon dioxide production and the significant reduction in the total DCE and FB discharged.

The microbial culture dynamics in both systems was monitored using Fluorescence in Situ Hybridisation (FISH) detected by fluorescent microscopy. Monitoring the microbial dynamics in the bioscrubber showed that when the absorber was not present cells activity and viability were negatively affected during the SAP experiments. Though, when the oil-absorber was introduced upstream to the bioscruber, FISH results confirmed that the negative effects were significantly reduced. Thus, the two specific degrading cultures were maintained active in the bioscrubber, which did not require any re-acclimation to the re-introduction of each substrate during sequential alternations in the pollutant feed between DCE and FB.

In general, the results of the present study have shown that the combined Oil-Absorber-Bioscrubber system is a robust technology, offering an effective solution to the biological treatment of waste-gas streams during SAP conditions of treatment.

[1] Ferreira Jorge RM, Livingston AG. 2000. Microbial dynamics in a continuous stirred tank bioreactor exposed to an alternating sequence of organic compounds. Biotechnol Bioeng 69:409-417.