Anaerobic biotechnology for industrial wastewater: Review

Abstract

Finally, engineering consultants and environmental engineering and science students and their teachers have a definitive book on anaerobic biotechnology. A major gap in environmental engineering textbooks existed for a long time in this area. The first three chapters provide a thorough overview of the anaerobic process in biological treatment, present foundations for understanding its application as explained in the latter part of the book, and compare it to aerobic technology. The anaerobic process is no longer an exotic system reserved for animal waste lagoons. There are close to 1000 full-scale anaerobic treatment plants worldwide. Many more plants of the lagoontype exist. The technology traditionally applied to concentrated industrial wastes is now being considered for dilute industrial wastewater, even sanitary sewage, as well as for solid waste in semi-dry form. Although the author stresses that he is aiming at waste streams containing colloidal matter, many items are directly applicable to all anaerobic processes, including sludge digestion (not specifically covered in the book). The book provides a very thorough literature review of individual topics. A detailed table of contents allows the readers immediate access to even small niches in the technology, e.g., separate subchapters on sulfide and ammonia toxicity and on inhibition and (or) biodegradation of individual chlorinated aromatics. The second chapter compares anaerobic and aerobic processes, loading rates, and retention times, with a short (too brief, in fact) discussion of economic considerations. Overall, in the book the subject of cost is not addressed adequately. Although rarely included in other textbooks, this information could enrich the book and help to make a stronger case for some engineers stil1 facing prejudice of the decision makers against anaerobic technology. In the third chapter, various kinetic expressions used in describing the impact of temperature and lack of nutrients and the role of sulfur and nitrogen in anaerobic corrosion are explained. Detailed stoichiometry of the off-gas and biomass production is illustrated, with particular reference to the acetate and hydrogen metabolisms. Chapters four and five cover operational considerations, treatability studies in lab and pilot scale, anaerobic toxicity assessment procedures, and techniques for determining the biomethanation potential of the waste. The importance of volatile fatty acids as intermediates and the particular role played by propionic acid are elucidated. Other operational issues such as interspecies hydrogen transfer, two-phase configuration, foaming, VFA accumulation, acclimation and monitoring strategies are also covered. Chapters six and seven cover biomass immobilization and concentrate on biomass washout and methods of preventing it. Issues of biological film and granule formation and factors affecting them in different reactor configurations are discussed. Chapters eight and nine concentrate on the effects of alkalinity and trace metals on the process, the cost of adding alkalinity, the stimulating role of some trace metals, and the inhibitory of others. Bio-availability of metals is discussed, as anaerobic conditions, particularly when sulfate/sulfide is present, create unfavorable conditions for trace metal uptake, due to metal binding. Chapter ten presents the methods of dealing with acute and chronic toxicity and inhibition. Although many reactive organics are toxic to un-acclimated biomass, proper control of the solids residence time can lead to biodegradation. A number of chloro-aromatics, chlorinated aliphatics, chloroform or trichloroethylene are routinely biotransformed anaerobically. Chapter eleven covers sulfide production, sulfide toxicity, and competition for substrate between the sulfate reducing bacteria and methanogens. The tolerance of methanogens to sulfide, the effects of acclimation and pH, as well as the role of the COD to sulfur ratio in driving the degradation process towards sulfide or methane are explained. The last chapter appropriately concentrates on fate and renewal of refractory organics. The issue of sequential anaerobic–aerobic treatment is mentioned briefly. The reviewer believes that sequential treatment where the anaerobic process precedes or follows aerobic treatment will become more important in the future as we gain more understanding of the biodegradation pathways. In summary, the book is a must for any engineer and scientist working with wastewater treatment, as it shows where anaerobic treatment fits best and how it should be applied. The Received October 2, 1996. Manuscript accepted November 18, 1996.