R.G.J. Edyvean

Treatment of tannery wastewater by chemical coagulation

Abstract The objective of this study was to develop a treatment system that can effectively reduce the concentration of pollutants in tannery wastewater to environmentally acceptable levels and that can greatly reduce the cost of discharging the effluents. Aluminium sulphate and ferric chloride were used as a coagulant in the process. The influence of pH and coagulant dosages on the coagulation process was studied and conditions were optimised corresponding to the best removal of organic matters, suspended solids as well as chromium. The COD and chromium were removed mainly through coagulation: 38–46% removal of suspended solids, 30–37% removal of total COD from settled tannery wastewaters and 74–99% removal of chromium at an initial concentration of 12 mg/l can be achieved by using the optimum coagulant dosage (800 mg/l) in the optimum pH range (around 7.5). Ferric chloride produced better results than aluminium sulphate. The initial chromium concentrations and pH values of the wastewater had a great effect on chromium removal efficiency. Low chromium concentrations and high pH produced a more effective result on chromium removal than high chromium concentrations and low pH. Higher dosages did not significantly increase pollutant removal and were not economical. Coagulation combined with centrifugation improved the removal efficiency of suspended solids (70%). A high degree of clarification is attained as indicated by an excess of 85–86% colour removal. The results provide useful information for tannery wastewater treatment.

Removal of coloured organic matter by adsorption onto low-cost waste materials

Abstract Twelve different adsorbents, originating from waste materials, were used to treat an effluent, of complex composition, from a chemical works. The effectiveness of each adsorbent was measured in terms of its effect on the colour (absorbance at 450 nm) and COD levels of the effluent and also in terms of its adsorption capacity towards individual constituents of the effluent. The results showed that all adsorbents would physically adsorb constituents in reversible processes. Some constituents were more readily adsorbed than others. This meant that little correlation was observed between changes to the colour and COD levels of the effluent, because individual constituents made different contributions to these properties. The problem is further complicated by adsorbents, particularly those which had not been processed, contributing new constituents to the effluent. Thermodynamic data obtained from this study were used to predict the relative distribution of three constituents on the surface of different adsorbents. These results suggest that, for this effluent, adsorption onto waste material would be most effectively applied by using it in combination with other removal techniques.

COMPARISON BETWEEN BIOSORBENTS FOR THE REMOVAL OF METAL IONS FROM AQUEOUS SOLUTIONS

This study compared the ability of a brown seaweed Ecklonia maxima, a dealginated seaweed waste, alginate fibre and waste linseed fibre to remove copper, nickel and cadmium from single and mixed metal ion solutions. All experiments were conducted using metal ion solutions of 10 mg/litre in concentration. The study has shown that alginate fibre generally exhibited the best overall metal ion uptake and cadmium ions were the most effectively sequestered by these biosorbents. The study indicates that the uptake of these metal ions is selective once saturation of the biosorbent has been achieved, with copper ions being adsorbed in preference to cadmium and nickel ions.

Characterization of the Cell Surface and Cell Wall Chemistry of Drinking Water Bacteria by Combining XPS, FTIR Spectroscopy, Modeling, and Potentiometric Titrations

Aquabacterium commune, a predominant member of European drinking water biofilms, was chosen as a model bacterium to study the role of functional groups on the cell surface that control the changes in the chemical cell surface properties in aqueous electrolyte solutions at different pH values. Cell surface properties of A. commune were examined by potentiometric titrations, modeling, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. By combining FTIR data at different pH values and potentiometric titration data with thermodynamic model optimization, the presence, concentration, and changes of organic functional groups on the cell surface (e.g., carboxyl, phosphoryl, and amine groups) were inferred. The pH of zero proton charge, pH(zpc) = 3.7, found from titrations of A. commune at different electrolyte concentrations and resulting from equilibrium speciation calculations suggests that the net surface charge is negative at drinking water pH in the absence of other charge determining ions. In situ FTIR was used to describe and monitor chemical interactions between bacteria and liquid solutions at different pH in real time. XPS analysis was performed to quantify the elemental surface composition, to assess the local chemical environment of carbon and oxygen at the cell wall, and to calculate the overall concentrations of polysaccharides, peptides, and hydrocarbon compounds of the cell surface. Thermodynamic parameters for proton adsorption are compared with parameters for other gram-negative bacteria. This work shows how the combination of potentiometric titrations, modeling, XPS, and FTIR spectroscopy allows a more comprehensive characterization of bacterial cell surfaces and cell wall reactivity as the initial step to understand the fundamental mechanisms involved in bacterial adhesion to solid surfaces and transport in aqueous systems.

Biofilm development on stainless steel in mains water

Biofilm development on stainless steel in mains water has been poorly documented to date. Results are presented of the development of potable-water biofilms over 12 months on stainless-steel grades 304 and 316, used as appendages to a large buildings plumbing distribution system. The viable cell counts on grade 304 pipe after 12 months averaged 2.8 × 103 cfu cm−2, compared to 3.6 × 102 cfu cm−2 on grade 316 pipe. The viable cell and total cell count on matt (2D) stainless steel remained significantly higher (p < 0.05) when compared to smooth (2B) stainless steel after 4-months and 8-months biofilm development, but at month 12 the viable cell counts on the two steel finishes were not significantly different. Total carbohydrate levels and biomass dry weight levels were slightly but not significantly higher on grade 304 than on grade 316. A mixture of biofilm bacteria attached to stainless steel were evident, including Pseudomonas spp., Methylobacterium spp., Acinetobacter spp., Corynebacterium/Arthrobacter spp. and Micrococcus spp. Inductively coupled plasma spectrophotometer analysis of biofilms showed an accumulation of metal ions in both grades 304 and 316 pipe biofilms. Molybdenum (0.04 mg litre−1) was found to be associated with biofilms isolated from grade 316 after 4 months, and 0.05 mg litre−1 was found in the biofilms after 12-months exposure to mains water. Scanning electron microscopy provided evidence of microcolony formation of rod-shaped and coccoid-shaped bacteria and diatoms.

Inhibition of biogas production and biodegradability by substituted phenolic compounds in anaerobic sludge.

Phenolic compounds are abundant in nature and organic wastes. This biomass may be utilised in biogas generation. Phenolics can inhibit the degradation of readily biodegradable organic fractions and their own biodegradation. In this work, assays were carried out under anaerobic conditions to study the inhibition of both gas production and biodegradability due to seven phenolic compounds and to study their adsorption onto sludge and autoxidation in the aqueous medium. Fifty percent inhibition was in the range of 120 to 594 mg of compound/g VSS. An initial enhancement followed by an inhibition of biogas formation was found. The inhibition by the phenolic compounds was found to be influenced by autoxidation, apolarity, type, size and number of substitutions. Biogas production is influenced by concentration rather than any pH change. The concentration of the phenolic compound was partially biomethanized and the degradation of gallic and caffeic acids by this process is reported here for the first time. The maximum total biodegradation of any phenolic compound was 63.85+/-2.73%, and remaining non-biodegradable fraction was autoxidized and adsorbed onto the sludge matrix. Inhibition of methanization and partial inhibition of background gas was found at concentrations between 800 and 1600 mg/L organic carbon.

The effect of turbulent flow and surface roughness on biofilm formation in drinking water

There is considerable interest in both Europe and the USA in the effects of microbiological fouling on stainless steels in potable water. However, little is known about the formation and effects of biofilms, on stainless steel in potable water environments, particularly in turbulent flow regimes. Results are presented on the development of biofilms on stainless steel grades 304 and 316 after exposure to potable water at velocities of 0.32, 0.96 and 1.75 m s−1. Cell counts on slides of stainless steel grades 304 and 316 with both 2B (smooth) and 2D (rough) finishes showed viable and total cell counts were higher at the higher flow rates of 0.96 and 1.75 m s−1, compared to a flow rate of 0.32 m s−1. Extracellular polysaccharide levels were not significantly different (P< 0.05) between each flow rate on all stainless steel surfaces studied. higher levels were found at the higher water velocities. the biofilm attached to stainless steel was comprised of a mixed bacterial flora including Acinetobacter sp, Pseudomonas spp, Methylobacterium sp, and Corynebacterium/Arthrobacter spp. Epifluorescence microscopy provided evidence of rod-shaped bacteria and the formation of stands, possibly of extracellular material attached to stainless steel at high flow rates but not at low flow rates.

The polymer physics and chemistry of microbial cell attachment and adhesion

The attachment of microbial cells to solid substrata is a primary ecological strategy for the survival of species and the development of specific activity and function within communities. An hypothesis arising from a biological sciences perspective may be stated as follows: The attachment of microbes to interfaces is controlled by the macromolecular structure of the cell wall and the functional genes that are induced for its biological synthesis. Following logically from this is the view that diverse attached cell behaviour is mediated by the physical and chemical interactions of these macromolecules in the interfacial region and with other cells. This aspect can be reduced to its simplest form by treating physico-chemical interactions as colloidal forces acting between an isolated cell and a solid or pseudo solid substratum. These forces can be analysed by established methods rooted in DLVO (Derjaguin, Landau, Verwey and Overbeek) theory. Such a methodology provides little insight into what governs changes in the behaviour of the cell wall attached to surfaces, or indeed other cells. Nor does it shed any light on the expulsion of macromolecules that modify the interface such as formation of slime layers. These physical and chemical problems must be treated at the more fundamental level of the structure and behaviour of the individual components of the cell wall, for example biosurfactants and extracellular polysaccharides. This allows us to restate the above hypothesis in physical sciences terms: Cell attachment and related cell growth behaviour is mediated by macromolecular physics and chemistry in the interfacial environment. Ecological success depends on the genetic potential to favourably influence the interface through adaptation of the macromolecular structure, We present research that merges these two perspectives. This is achieved by quantifying attached cell growth for genetically diverse model organisms, building chemical models that capture the variations in interfacial structure and quantifying the resulting physical interactions. Experimental observations combine aqueous chemistry techniques with surface spectroscopy in order to elucidate the cell wall structure. Atomic force microscopy methods quantify the physical interactions between the solid substrata and key components of the cell wall such as macromolecular biosurfactants. Our current approach focuses on considering individually mycolic acids or longer chain polymers harvested from cells, as well as characterised whole cells. This approach allows us to use a multifactorial approach to address the relative impact of the individual components of the cell wall in contact with model surfaces. We then combine these components to increase complexity step-wise, while comparing with the behaviour of entire cells. Eventually, such an approach should allow us to estimate and understand the primary factors governing microbial cell adhesion. Although the work addresses the cell-mineral interface at a fundamental level, the research is driven by a range of technology needs. The initial rationale was improved prediction of contaminant degradation in natural environments (soils, sediments, aquifers) for environmental cleanup. However, this area of research addresses a wide range of biotechnology areas including improved understanding of pathogen survival (e.g., in surgical environments), better process intensification in biomanufacturing (biofilm technologies) and new product development.

Biofouling: an historic and contemporary review of its causes, consequences and control in drinking water distribution systems

Biofouling in water distribution systems has, arguably, affected our lives for more than 3500 years. It may be defined as the undesirable accumulation of biotic matter on a surface, which can cause odour and taste problems, the deterioration of pipe materials and fittings and result in the discoloration of water. Early efforts to combat these problems included the use of sedimentation tanks, disinfection by silver ionization and cleaning of the distribution network. At the turn of the nineteenth century, rapid sand filtration and water disinfection became widely used and helped to reduce the organic and bacterial load in drinking water. A better understanding of the role and causes of biofouling in water distribution systems resulted in various legislations, which in turn have been a driving factor for improving or developing new water treatment methods, pipe materials, analytical techniques, etc. However, increasing requirements on water quality in the late twentieth century made water treatment and specific anti-corrosion and/or microbial control regimens insufficient as a means of solving the transportation problem owing to the heterogeneity of pipe materials and contamination from outside the distribution system. Furthermore, as drinking water passes through the mains it undergoes a series of quality changes owing to interactions with the pipe walls, bacteria and the sediment phase. This review emphasizes the extent to which biofouling depends on interactions between microorganisms and (1) nutrients, (2) environmental conditions (temperature), (3) physicochemical processes (sedimentation, corrosion, disinfection) and (4) pipe material. A good knowledge of these complex interactions is necessary for implementing a successful biofouling control strategy.

Biologically enhanced corrosion fatigue

Corrosion fatigue is considered to be one of the most important factors in determining the life of static offshore structures such as platforms for oil and gas production; the combination of corrosive environment and cyclic stress can produce failure of metals by the development and growth of cracks. Seawater provides both the chemical reagent and, through wave action, the source of cyclic fatigue loading. Marine fouling can enhance both factors, first by enhancing the corrosive reactions and secondly by increasing the diameter and surface roughness of platform legs and bracing members. In relation to corrosion fatigue this enhancement is mainly due to the production of hydrogen sulphide by sulphate‐reducing bacteria. Both the effects of loading and hydrogen embrittlement can be independent of anti‐corrosion measures and thus need to be quantified and incorporated into the determination of the design life of the structure. Data are presented on the level of hydrogen sulphide that could be found under mari...