SummaryExperimental evidence is presented which indicates t8hat both chemical and autoflocculation of microorganisms occur by the same mechanism. Basically, long chain polymeric species attach themselves between the microbial particles and agglomerate them into flocculant particles of sufficient magnitude to subside from suspension under quiescent conditions. Properties of the polymers which are produced during autoflocculation are investigated and these polymers are shown to be capable of causing the agglutination of inorganic colloids such as alumina. It is hypothesized that these biologically generated flocculating polymers could belong to a class of compounds known as transport enzymes. The experimental data qualitatively agrees with this hypothesis.Biological treatment systems currently are used extensively in the treatment of domestic and industrial wastewaters. Aerobic heterotrophic systems (e.g., activated sludge, trickling filters) are conventionally used for the removal of organic pollutants as are anaerobic heterotrophic systems (e.g., anaerobic digesters, anaerobic lagoons). Autotrophic systems (e.g., algal ponds, lagoons) are utilized for the removal of inorganic pollutants such as nitrogeneous and phosphatic compounds. Combined autotrophic heterotrophic systems (e.g. , oxidation ponds, activated algal systems) have also been successfully employed for the concurrent removal of organic and inorganic impurities from wastewater.The two basic design considerations of any biological wastewater treatment system are: 1) providing environmental conditions satisfactory for the removal of pollutants from the wastewater by the metabolic activities of the microorganisms, and

The feasibility of removing algae from water and wastewater by chemical flocculation techniques was investigated. Mixed cultures of algae were obtained from both continuousand batch-fed laboratory reactors. Representative cationic, anionic, and nonionic synthetic organic polyelectrolytes were used as flocculants. Under the experimental conditions, chemically induced algal flocculation occurred with the addition of cationic polyelectrolyte, but not with anionic or nonionic polymers, although attachment of all polyelectrolyte species to the algal surface is shown. The mechanism of chemically induced algal flocculation is interpreted in terms of bridging phenomena between the discrete algal cells and the linearly extended polymer chains, forming a three-dimensional matrix that is capable of subsiding under quiescent conditions. The degree of flocculation is shown to be a direct function of the extent of polymer coverage of the active sites on the algal surface, although to induce flocculation by this method requires that the algal surface charge must concurrently be reduced to a level at which the extended polymers can bridge the minimal distance of separation imposed by electrostatic repulsion. The influence of pH, algal concentration, and algal growth phase on the requisite cationic flocculant dose is also reported.

The feasibility of removing algae from water and wastewater by chemical flocculation techniques was investigated. Mixed cultures of algae were obtained from both continuous- and batch-fed laboratory reactors. Representative cationic, anionic, and nonionic synthetic organic polyelectrolytes were used as flocculants. Under the experimental conditions, chemically induced algal flocculation occurred with the addition of cationic polyelectrolyte, but not with anionic or nonionic polymers, although attachment of all polyelectrolyte species to the algal surface is shown. The mechanism of chemically induced algal flocculation is interpreted in terms of bridging phenomena between the discrete algal cells and the linearly extended polymer chains, forming a three-dimensional matrix that is capable of subsiding under quiescent conditions. The degree of flocculation is shown to be a direct function of the extent of polymer coverage of the active sites on the algal surface, although to induce flocculation by this method requires that the algal surface charge must concurrently be reduced to a level at which the extended polymers can bridge the minimal distance of separation imposed by electrostatic repulsion. The influence of p H, algal concentration, and algal growth phase on the requisite cationic flocculant dose is also reported.

SummaryThe mixing of the anaerobic digester contents significantly influences the efficiency of this operation; in particular, hydraulic dead zones are extremely detrimental to the reaction kinetics involved in anaerobic digestion. An analysis of the relative importance of thermal fluid movement in the digester to those caused by fluid inflow and outflow is presented. As an example, these principles are applied to a digester a t the South Bend Wastewater Treatment Plant. Experimental measurements, which have general applicability for the measurement of digester mixing volume, confirm the theoretical conjectures. Various types of optimizations can be attempted on this mixing operation. One such optimization applied to gas lift mixers, as employed in the South Bend Treatment Plant, is illustrated.

SummaryPresently empirical expressions, especially the Monod equation, are used to quantitatively relate microbial growth rate to limiting substrate concentration in the solution. In this paper microbial growth is postulated to occur by a mechanism involving a mass transfer or assimilation process and an ingestion and cell division process. The assimilation process is assumed to be substrate mass transfer limited and hence proportional to the limiting substrate concentration. The ingestion is assumed independent of limiting substrate concentration and only dependent upon internal reaction rates. The quantitative relationship between limiting substrate and microbial growth rate resulting from this mechanism is developed. Under certain limiting conditions this expression is shown to reduce to the Monod equation and under other conditions it reduces to the LotkaVolterra relationship. This mechanism is applied to batch and continuous cultures and the results obtained are compared qualitatively with experiment.The principal mathematical expression used to relate rate of microbial cell growth to limiting substrate concentration is the Monod equation' which is analogous to the Michaelis-Menten equation for enzymatic reactions. This equation is accepted primarily because it qualitatively resembles the experimentally measured relationship and it is easy to use. However, it is recognized that there are many cases in which observed values of cell concentration do not correspond to those predicted by this equation in batch cultivation. I n particular, this expression does not predict the lag phase, nor does it predict the endogenous phase of batch cultivation. In continuous cultivation, this equation rarely predicts the experimental results, partly because the yield of cell mass from limiting substrate is not