R.J. Martin

Ecological equilibrium on biological activated carbon

This paper examines the potential of a biological activity control system (BACS) for biological activated carbon (BAC) in comparison to granular activated carbon (GAC) for the treatment of potable water. The overall objective of the project is to produce drinking water of a higher quality more economically by developing a BACS for exhausted GAC that can be transformed to BAC by the development of a natural biofilm during the bio-regeneration mode. The research therefore may be interesting for water companies and the activated carbon industry. Findings show that the lifetime of a GAC filter can be significantly extended by maintaining an active biofilm that has to be controlled in order to avoid filter clogging. The most important parameters are dissolved oxygen (DO), pH and a correct balance of nutrients, which enables a natural control of the biomass. pH control was required to maintain an optimal bacteria-protozoa level. Excessive growth of filamentous bacteria can be prevented by a decrease in DO, increase in pH and the reduction of one essential nutrient, e.g. total phosphorus (P). Total organic carbon (TOC) and chemical oxygen demand (COD) values were reduced by bioactivity. DO, turbidity and suspended solids (SS) values were kept in acceptable ranges with respect to drinking water objectives. Plants without a significant population of protozoa deliver turbid low quality effluent high on SS and biochemical oxygen demand (BOD). It was possible to control the biofilm on GAC containing a natural biofilm and BAC during the bio-regeneration mode. Natural and artificial bio-regeneration lead to similar performance characteristics.

Chemical regeneration of exhausted activated carbon—I

Abstract This paper represents the first of a series of reports on the chemical regeneration of exhausted activated carbon following experimental research studies carried out at the University of Birmingham, U.K. A wide range of regenerants, inorganic and organic, was evaluated in the treatment of carbon samples exhausted with mono-substituted benzene compounds. Organic chemical regenerants with solubilising powers were found to be generally much more effective than inorganic chemical regenerants with oxidising powers. Results showed that the efficacy of organic solubilising regenerants decreased as their molecular weights and sizes increased; it is likely that the smaller the regenerant, the further it could penetrate into the micropores of the carbon and displace the adsorbate. The relationship between the molecular weight of the adsorbate and that of the organic regenerant was observed to be of significant importance; the regenerant chosen should be smaller than the smallest adsorbate to be removed.

The repeated exhaustion and chemical regeneration of activated carbon

Abstract Following experimental research studies carried out at the University of Birmingham, U.K., this paper presents data on the repeated application of the cycle of exhaustion, chemical regeneration and re-exhaustion of activated carbon. The adsorbates studied were nitrobenzene (a small organic molecule of mol. wt approx. 123), Rhodamine B (a much larger adsorbate of mol. wt approx. 480) and humic acid (an ill-defined substance consisting of macromolecules of molecular weight predominantly in the range 20,000–50,000). The regenerants used were all organic with solubilising powers to encourage the physical displacement of the adsorbate molecule by the regenerant molecule. As a general conclusion, it may be stated that chemical regenerants could be used to regenerate granular activated carbon repeatedly with little loss of adsorption capacity. Earlier studies which considered the effect of water on the powers of the carboxylic acid regenerants were confirmed in the results reported here. Bonding between the acids and water hindered the regeneration process.

Adsorption studies using gas-liquid chromatography—1. effect of molecular structure

Abstract Gas-liquid chromatography (GLC) with a flame ionization detector system using the direct injection of aqueous solutions was used to monitor the adsorption of selected organic compounds dissolved in water onto activated carbon. The effects of the introduction of NH 2 , OH, CH 2 OH and NO 2 groups to the benzene ring, the introduction of a second benzene ring. OCH 3 , Cl, CH 3 and NO 2 groups to phenol and the effect of substituted positions on adsorption were investigated. The adsorption of some heterocyclic compounds and the effect of the introduction of a benzene ring or CH 3 to these heterocyclics were also investigated. Hydrogen bonding and steric hindrance were observed to be significant factors in the adsorption process.

Adsorption studies using gas-liquid chromatography—II. Competitive adsorption

Abstract Gas-liquid chromatography with a flame ionization detector system using the direct injection of aqueous solutions was used to monitor the adsorption of selected organic compounds dissolved in water onto activated carbon. The effects of competitive adsorption in batch (agitated flask) and column (flow through packed bed) systems were investigated. The effects became more pronounced with increase in the number of solutes in solution. This emphasises the importance of the competitive adsorption effect on the performance of an activated carbon unit in water or wastewater treatment.

The effects of pH and suspended solids in the removal of organics from waters and wastewaters by the activated carbon adsorption process

Abstract The effects of pH, inorganic suspended solids and organic suspended solids on the adsorption of organics by activated carbon were investigated using sewage effluents and selected organic compounds of varying size, structure, molecular weight and properties in model solutions. It was found that suspended solids, and in particular organic suspended solids, could interfere with the adsorption process, both in terms of adsorption capacity and adsorption rate; the effect of the solids diminished as the size of the adsorbate increased. The effect of pH variation became more significant as the acidity or basicity of the adsorbate in solution increased. Adsorption of organics from biologically treated sewage effluents was somewhat more effective in the acid and alkaline pH regions than in the neutral pH region.

Adsorption studies using gas-liquid chromatography—IV. Adsorption from bisolute systems

Abstract Gas-liquid chromatography with a flame ionization detector system using the direct injection of aqueous solutions was used to monitor the adsorption of selected organic compounds dissolved in water onto activated carbon. The effects of competitive adsorption in bisolute solution systems were investigated. In general, the higher molecular weight compound was more favourably adsorbed because of the higher affinity of the larger molecule to the carbon surface.

Comparison of two partially activated carbon fabrics for the removal of chlorine and other impurities from water

Abstract Experimental studies were undertaken at the University of Birmingham to investigate and compare the use of two partially activated carbon fabrics for the removal of chlorine and other impurities from potable water in domestic point-of-use water filters. Since the implementation of the EEC drinking water quality directive in July 1985, there has been a marketing surge in domestic water filters, generally aimed at improving taste (the taste of chlorine is frequently cited). The fabrics were observed to be very effective at removing chlorine from water; their dechlorinating powers were significantly superior to that of the granular activated carbon used for comparison. The fabrics were observed to be much less effective at removing phenol, methylene blue and colour.