C.F. Forster

Study of the Sorption of Divalent Metal Ions on to Peat

A pseudo-second order rate equation describing the kinetics of sorption of divalent metal ions on to sphagnum moss peat at various initial metal ion concentrations and peat doses has been developed. The sorption kinetics were followed based on the concentrations of metal sorbed at various time intervals. Results show that chemical sorption processes might be rate-limiting for the sorption of divalent metal ions on to peat during agitated batch contact time experiments. The rate constant, the equilibrium sorption capacity and the initial sorption rate were calculated. From these parameters, an empirical model for predicting the concentrations of metal ions sorbed was derived.

A comparative study of the nature of biopolymers extracted from anaerobic and activated sludges

Abstract The chemical nature of sludge extracellular polymers are widely reported as being influential in determining many of the physico-chemical properties of sludges. A comparison was made between biopolymers extracted from activated and anaerobic sludges including UASB granules. Noticeable differences as to the total yield of ECP/(g SS) were observed. Activated sludge samples produced 70–90 mg ECP/(g SS) compared with 10–20 mg ECP/(g SS) for granular sludge. A relationship between the concentration of ECP extracted and the surface charge of the sludge solids was observed. Activated sludges were found, using a colloid titration technique, to be more electronegative than granular sludges. Gross chemical analysis of these extracted polymers suggests that anaerobic and activated sludge polymers do differ, with protein being the most dominant fraction in anaerobic samples compared with carbohydrate in the latter. The relative concentrations of elements present in the ashed extracts, measured by EDAX, show a predominance of phosphorus and calcium. The actual concentrations of these two elements were found to be greatest in the extracts from the anaerobic granules and anaerobic fluidised bed biofilm.

Kinetic studies of competitive heavy metal adsorption by sphagnum moss peat

Much of the work on the adsorption of metals by low-cost, natural biosorbents has focussed on the uptake of single metals. In practice, wastewaters are polluted with multiple metals. In addition, the kinetics of adsorption, which are important in the design of treatment systems, have largely been neglected. This paper describes the results of an examination into the adsorption by peat of copper and nickel from both mono and bi-solute systems. These showed that, in general, pore diffusion appeared to be the rate-controlling step and that the presence of ‘contaminant’ copper ions reduced the binding of nickel. In fact, the best interpretation which could be placed on the data was that the behaviour of nickel was unusual. The results also showed that the kinetics of adsorption were best described by a second-order expression rather than a first-order model.

Continuous co-digestion of cattle slurry with fruit and vegetable wastes and chicken manure

Abstract Anaerobic digestion is a well established process for treating many types of organic waste, both solid and liquid. As such, the digestion of cattle slurries and of a range of agricultural wastes has been evaluated and has been successful. Previous batch studies have shown that based on volatile solids (VS) reduction, total methane production and methane yield, co-digestions of cattle slurry (CS) with fruit and vegetable wastes (FVW) and with chicken manure (CM) were among the more promising combinations. A continuously stirred tank reactor ( 18 litres ) was used as a mesophilic (35°C) anaerobic reactor to examine the effect of adding the FVW and CM to a system which was digesting CS. The retention time was kept at 21 days and the loading rate maintained in the range 3.19– 5.01 kg VS m −3 d −1 . Increasing the proportion of FVW from 20% to 50% improved the methane yield from 0.23 to 0.45 m 3 CH 4 kg −1 VS added, and caused the VS reduction to decrease slightly. Increasing the proportion of chicken manure in the feed caused a steady deterioration in both the criteria for judging digester performance. This appeared to be caused by ammonia inhibition.

Batch nickel removal from aqueous solution by sphagnum moss peat

Abstract The batch adsorption of Ni(II) onto sphagnum moss peat has been studied. The reaction was pH dependent, the optimum range being 4.0–7.0. Langmuir and Freundlich isotherms, established for various initial nickel concentrations and for a range of pH values, were used to obtain a single relationship between initial metal concentration, metal removal, and initial pH. The latter was found to control efficiency of nickel removal. Kinetic data suggested involvement of a chemical rate-limiting step, and a predictive relationship was derived relating nickel removal to peat dose. In comparison with other metals, nickel removal is poor, and possible reasons are discussed.

Removal of hexavalent chromium using sphagnum moss peat

Abstract Batch adsorption studies have shown that sphagnum moss peat, which is essentially oligotrophic, in concentrations ranging from 4 to 40 g/l can be used effectively to remove hexavalent chromium from aqueous solutions. The process is pH dependent, the optimum range being 1.5-3. Treatment of the exhausted peat with 1 M NaOH removed only 50% of the sorbed metal, suggesting that the binding to the peat involved strong chemisorption forces.

A preliminary examination into the adsorption of hexavalent chromium using low-cost adsorbents

Abstract Four organic wastes were tested as potential adsorbents for hexavalent chromium. The results showed that this type of material could certainly be considered for this purpose with the best results being achieved at pH values of 1·5–3·0. The results showed that cellulosic materials which had been subjected to some degree of anaerobic biodegradation were better adsorbents than fresh cellulosic material.

Co-digestion of waste organic solids: batch studies

Anaerobic digestion is a well established process for treating many types of organic waste, both solid and liquid. As such, the digestion of cattle slurries and of the organic fraction of municipal solid waste has been evaluated and has been successful. Attempts to apply the process to other types of solid organic waste, for example, to chicken manure, have met with limited success. In many areas of the UK, intensive chicken farming is leading to solids disposal problems. It has been proposed that co-digestion with cattle slurry could be a possible disposal route for chicken manure. In this study, cattle slurries were mixed with a range of solid wastes and allowed to digest in 1-1 batch digesters. The criteria for judging the success of a co-digestion were volatile solids (VS) reduction, total methane production and methane yield. In terms of the VS reductions (%), there was little difference between the various digestions. In terms of the cumulative methane production (1) the co-digestions with fruit and vegetable waste, the fish offal and the dissolved air flotation sludge were more effective than the digestion with cattle slurry alone. In terms of the specific methane yield (m3 CH4 kg−1 VS removed), the co-digestions containing fish offal and the brewery sludge gave higher values than the control digestion with cattle slurry alone. Compared with their control (cattle slurry alone), both co-digestions with poultry manure (7.5 and 15% TS) gave higher cumulative productions of methane and the system with the lower concentration of poultry manure gave a higher specific methane yield. However, there was some evidence of ammonia inhibition.

Heavy metal adsorption characteristics of a submerged aquatic plant (Myriophyllum spicatum)

Submerged aquatic plants can be used for the removal of heavy metals. In this paper, the adsorption properties of Myriophyllum spicatum (Eurasian watermilfoil) for lead, zinc, and copper were investigated and the results were compared with other aquatic submerged plants. Data obtained from the initial batch adsorption studies have indicated that M. spicatum is capable of removing lead, zinc, and copper from solution. Metal biosorption was fast and equilibrium was attained within 20 min. Data obtained from further batch studies fitted the Langmuir model. The maximum adsorption capacities (qmax) were 10.37 mg/g for Cu(II), 15.59 mg/g for Zn(II) and 46.49 mg/g for Pb(II). The kinetics of adsorption of zinc, lead and copper were also analysed and rate constants were derived for each metal. It was found that the overall adsorption process was best described by the pseudo second order kinetics. The results showed that this submerged aquatic plant M. spicatum can be successfully used for heavy metal removal.

THE POTENTIAL FOR BIOFILM GROWTH IN WATER DISTRIBUTION SYSTEMS

Biofilms on pipe walls in water distribution systems are composed of bacteria in a polymeric matrix, which can lead to chlorine demand, coliform growth, pipe corrosion and water taste and odour problems. The majority of previous studies have been laboratory or pilot plant based and few results are available for field conditions. In this study, field observations of biofilm were made using biofilm potential monitors. The monitor results were compared with pipe samples taken from the distribution system and with laboratory pipe reactors. An empirical equation quantified the inhibitory effects of free chlorine and decrease of temperature on biofilm growth. With water having total organic carbon concentrations in the range 1.5-3.9mg/1 a free chlorine residual of 0.2 mg/l was needed to reduce biofilm concentration to below 50 pg ATP cm2. Pipe material influenced biofilm activity far less than chlorine with mean biofilm activity being ranked in the order glass (136 pg ATP/cm2) < cement (212 pg ATP/cm2) < MDPE (302 pg ATP/ cm2) < PVC (509 pg ATP/cm2).