William G. Characklis

Corrosion of mild steel under anaerobic biofilm

Abstract Corrosion of mild steel under completely anaerobic conditions in the presence of a mixed population biofilm, including sulfate-reducing bacteria (SRB), has been studied in a continuous flow system. The closed channel flow reactor was continuously fed with low concentration substrate at different dilution rates that influenced biofilm accumulation. No direct correlation was observed between corrosion and SRB activity in the absence of ferrous iron. Furthermore, corrosion of mild steel in the SRB environment was determined by the nature of the metal and environmental conditions such as dissolved iron concentration. When formation of an iron sulfide film on mild steel was prevented before the biofilm accumulated, the metal surface retained its scratch lines after a 21-day experiment (SRB at 2.6 × 109/cm2). However, when the iron sulfide film was formed before the accumulation of biofilm, visible localized corrosion appeared after 14 days and increased up to 21 days. Intergranular and pitting attack ...

Biofilm development: a process analysis

This paper will provide a framework for understanding the process of biofilm development in the context of stoichiometry and kinetics. Biofilm development is described in terms of selected fundamental rate processes and environmental parameters which influence their rate and extent. The properties of the biofilm and its microenvironment lead to topics of microbial ecology within the biofilm and the physiology of the organisms immobilized within it. These topics will be discussed in terms of unstructured models for the microbial processes.

Influence of Fouling Biofilms on Heat Transfer

In heat exchange equipment, fouling biofilm formation causes a significant energy loss by increasing heat transfer resistance. This paper describes experiments which quantify the influence of fouling biofilms on heat transfer resistance under controlled laboratory conditions. Experimental results compare well with a rather simple mathematical model employing friction factor, biofilm thickness, wall temperature, bulk temperature, and fluid properties as inputs. Limitations of the experimental apparatus and mathematical model are discussed

Fate of cyanide and related compounds in aerobic microbial systems—II. Microbial degradation

Abstract Cyanide metabolism was studied using starved, acclimated heterogeneous cultures in an aerated microfermenter containing glucose as substrate. Tests using K 14 CN indicated that up to 50% of the cyanide was metabolized as evidenced by 14 CO 2 production. Experiments employed initial solids concentrations between 483–1963 mg l and initial glucose concentrations between 100–600 mg l. Initial cyanide concentration was 10 mg l.

Biofouling: effects and control

Biofouling refers to the undesirable accumulation of a biotic deposit on a surface. The deposit may contain micro- and macroorganisms. The focus of this paper is microbial fouling biofilms which consist of an organic film composed of microorganisms embedded in a polymer matrix of their own making. The composite of microbial cells and EPS is termed a biofilm. The surface accumulation is often composed of significant quantities of inorganic materials. Complex fouling deposits, like those found in industrial environments, often consist of biofilms in intimate association with inorganic particles (1), crystalline precipitates or scale (2), and/or corrosion products (3). These complex deposits often form more rapidly and are more tightly bound than biofilm alone. These deposits are difficult to characterize at the microscale, i.e. at the cellular level.

Mass and heat transfer in a circular tube with biofouling

Abstract A mathematical model of heat and mass transfer for a fluid flowing in a hollow cylinder with a tubular biofilm is developed. Results in dimensionless form are presented for mass transfer in isothermal laminar and turbulent flow and for heat transfer and combined heat-mass transfer in turbulent flow. For each system, the dominant resistance to the transport of heat and mass is determined. In a typical heat exchanger, the presence of a biofilm is found to decrease heat transfer significantly. For systems of interest, the biofilm thickness is nearly constant over the length of the tube in isothermal turbulent flow. In tubes with combined heat and mass transfer the thickness varies appreciably with the temperature of the fluid.

Fate of cyanide and related compounds in aerobic microbial systems—I. Chemical reaction with substrate and physical removal

Abstract The chemical reaction of cyanide with substrate was investigated in sealed glass ampoules using glucose as substrate and inorganic buffers. The reaction was found to be pseudo-first order and pH dependent, with an optimum pH near 11.0. The cyanide-glucose reaction products were found to be biodegradable by both acclimated and unacclimated heterogeneous cultures in shake flask and BOD bottle systems. Adsorption onto microbial solids was investigated using sealed, stirred glass reactors containing bacteria and potassium cyanide in water buffered at pH 7.0 with inorganic buffers. Very little adsorption occurred on a starved non-flocculating pure culture of Bacillus megaterium , although up to 15% adsorption occurred in systems containing a stirred flocculent heterogeneous culture. Stripping was investigated from a starved heterogeneous culture in an aerated microfermenter at neutral pH. Hydrogen cyanide and carbon dioxide in the off-gas were trapped in sodium hydroxide solution, separated and analyzed. Stripping removed up to 80% of original cyanide, and tests using K 14 CN revealed that a small amount of cyanide had been metabolized.

TEMPERATURE DEPENDENCY OF MICROBIAL REACTIONS

ABSTRACT The influence of temperature on the stoichiometry and rate of microbial processes is reviewed. Microbial rate processes are segregated into more fundamental processes such as mass transfer, biomass production, biomass decay and substrate uptake to provide a more systematic basis for analysis. The application of the techniques to determine temperature dependence of several unit processes is demonstrated with case studies based on published data.

A study of stormwater runoff quality

Abstract The stormwater from four watersheds in the Houston area was monitored by an intensive sampling and analytical program over a three year period. The land use in the watersheds included undeveloped forest, developing forest, fully developed residential and mixed commercial-residential. Chemical parameters monitored included suspended solids, oxygen demand, organic carbon, nitrogen, phosphorous, dissolved oxygen, pH, specific conductance and chlorinated hydrocarbons. Indicator and pathogenic bacterial content were enumerated as well as aguatic and edaphic algae species. Disinfectant demand and algal bioassays were also conducted. Relationships have been developed between stormwater runoff quality, quantity and land use in an effort to predict pollutant loads. The appearance of a “first flush” is dependent on the parameter measured and the watershed characteristics. Rainwater quality contributes significantly to stormwater pollutant load, especially in urbanized areas. The modifying effect of natural biological processes on nitrogen content in the runoff and the effects of the hydrological regime on nutrient limitations has been observed. The effectiveness of storage lakes, very positive in the case of suspended solids, has been described.