D.F. Toerien

The effect of carbon on algal growth—Its relationship to eutrophication

Abstract The literature has been reviewed to obtain a proper perspective on the role of carbon in natural aquatic ecosystems and to provide a comprehensive picture of carbon interactions (physical, chemical, and biological)in aquatic systems. Discussion of the carbon cycle comprises the processes of synthesis, degradation, and excretion of organic carbon compounds and the role of various microorganisms in these processes. Inorganic carbon chemistry is developed with specific emphasis on alkalinity components, buffering, chemical and biological reaction rates, and carbonic anhydrase activity. Organic and inorganic carbon utilization by algae and comparison of natural aquatic systems with laboratory and wastewater treatment systems are considered in relation to the question of algal growth. The final sections consider nutrient utilization by algae and the role of carbon in eutrophication processes. The overall conclusion of this review is that carbon will rarely if ever be limiting in natural environments.

The proteolytic bacteria present in the anaerobic digestion of raw sewage sludge

Abstract The occurrence and identity of proteolytic bacteria in the anaerobic digestion of raw sewage sludge were investigated. Proteolytic bacteria occurred in numbers of 65 × 106/ml. A high proportion of the isolates (65 per cent) was sporeforming bacteria, and included seven Clostridium species. Cocci comprised 21 per cent of the isolates and consisted mainly of Peptococcus anaerobius and one isolate of Staphylococcus aureus. The remaining isolates were non-sporeforming rod-shaped bacteria and included bifid-like bacteria, Bacteroides species and Eubacterium species.

A biological and chemical study of several anaerobic digesters

Abstract Biological and chemical analyses were carried out on several digesters operated on laboratory, pilot and full-scale. These digesters received a variety of substrates which included raw sewage sludge, industrial effluents and a synthetic substrate. Hexose monophosphate shunt enzymes could only be demonstrated in very active digesters receiving substrates high in carbohydrate material. The glycolytic pathway, glyoxylic acid and citric acid cycles were found in all the anaerobic digesters analysed. Enzyme activity tests revealed different stages of adaptation of a raw sewage digester adapted to a synthetic substrate. Digesters receiving different substrates showed characteristic enzyme activity patterns, but chemical analysis such as pH, alkalinity and volatile fatty acid content did not demonstrate any obvious differences between these digesters.

The bacterial nature of the acid-forming phase of anaerobic digestion

Abstract During bacteriological studies on several laboratory-scale digesters aerobic and facultative anaerobic bacteria occurred in all digesters at all stages, but numerically these bacteria were found to comprise less than 1 per cent of the total acid-forming bacterial population. Obligate anaerobic acid-forming bacteria were also found in all digesters at all stages, usually in numbers 100–200 times greater than the aerobic and facultative anaerobic bacteria present. The numbers of the obligate anaerobic acid-forming bacteria were highly significantly correlated with the deoxyribonucleic acid (DNA) and volatile suspended solids (VSS) contents of the anaerobic digesters. The same was not true for the aerobic and facultative anaerobic bacteria. A highly significant correlation between DNA and VSS was also observed. It was concluded that the concept that facultative anaerobic bacteria are the most important acid producers in anaerobic digestion is incorrect, and that obligate anaerobic bacteria are the important group in acid production.

Biological changes during the adaptation of an anaerobic digester to a synthetic substrate

Abstract A study of the biological changes taking place in the heterogenous microbial population of an anaerobic digester during the period of adaptation to a synthetic substrate and the procedure used to adapt the population to the new substrate is described. Adaptation from raw sewage sludge to the new substrate was followed by chemical, enzymic and bacteriological analyses of the liquid and the solid phases in the digester. Results indicate that although the chemical composition of the effluent did not show any significant changes over the period of adaptation, the chemical, enzymic and bacteriological properties of the sludge phase changed markedly. Results also indicate that adaptation to the new substrate was not complete after 60 days operation since the microbial population was still changing as indicated by intermediate enzyme activities and the number of micro-organisms present per unit volume.

Enrichment culture studies on aerobic and facultative anaerobic bacteria found in anaerobic digesters

Abstract Enrichment culture studies were undertaken to determine which aerobic and facultative anaerobic bacteria participate in anaerobic digestion, in the degradation of cellulose, starch, casein, peptone and sunflower oil. Each carbon source stimulated the development of a typical bacterial population. Facultative anaerobic bacteria such as Bacillus spp. may possibly contribute towards the primary liquefaction of macromolecules, while pseudomonads, coliforms and gram positive cocci probably play a secondary role in the degradation of substances such as cellulose and lipids.

A method for the enumeration and cultivation of anaerobic “acid-forming” bacteria present in digesting sludge

Abstract A method is described for the enumeration and cultivation of anaerobic “acid-forming” bacteria from digesting sludge. In this method use is made of pre-reduced media in roll tubes containing oxygen-free gas atmospheres. Digester supernatant liquor is included in the culture media to provide the growth factors normally present in anaerobic digesters.

Interrelations between biological and chemical characteristics in anaerobic digestion

Abstract A thorough study of the ecosystem of anaerobic digestion should include determinations of both biotic and environmental characteristics and the interrelations between these characteristics. This paper describes such a study executed on three experimental laboratory-scale digesters receiving limiting amounts of nitrogen in their substrate. The characteristics of these three digesters were followed daily until failure of digestion occurred as a result of a deficiency in nitrogen. The daily observations included gas production data, chemical quality determinations, counts of different groups of bacteria, and the determination of a wide range of intermediary metabolic enzymes. The changes taking place in these characteristics until failure occurred are discussed. Linear correlation coefficients were determined between all the different characteristics. A large number of significant correlations was found between the different characteristics of the ecosystem. The implications of some of these correlations are discussed, as well as the advantages of such an approach to the study of ecosystems in general.

Enumeration, isolation and identification of sulphate-reducing bacteria of anaerobic digestion

Abstract A method was developed for the enumeration and isolation of the sulphate-reducing bacteria in the anaerobic digestion of raw sewage sludge. This method differed from conventional methods used for the enumeration and isolation of sulphate-reducing bacteria in that anaerobiosis was achieved by the use of media with a low redox potential in stoppered bottles containing oxygen-free gas atmospheres. Carbon dioxide—bicarbonate buffer systems were employed in the media. Sulphate-reducing bacteria occurred in numbers of 3–5 × 10 4 /ml in a raw sewage sludge digester. Seven pure cultures of sulphate-reducing bacteria were isolated from digesters and all proved to be Desulfovibrio desulfuricans . No evidence for the presence of Desulfotomaculum ssp. was found. The role of sulphate-reducing bacteria in the anaerobic digestion of raw sewage sludge is discussed.

Algal growth prediction using growth kinetic constants

Abstract The growth kinetics under conditions of phosphorus limitation of Selenastrum capricornutum Printz, a green alga specified for use in algal bioassays, were used to predict growth in batch cultures for varied specific conditions of time and phosphorus concentration. These predictions compared very well with actual batch culture growth studies. The predicted maximum cell concentration for two different levels of phosphorus lay within values obtained in different laboratories. The predicted maximum specific growth rates ( μ ) were either close to or just above actual laboratory data. The determination of growth kinetics thus allows accurate prediction of the growth of planktonic algae, a benefit in either algal bioassays or the solution of practical eutrophication problems. The growth kinetic constants of specific algae important in eutrophication problems need to be determined in order to utilize potentialities of prediction in the rational solution of these problems.