Dec 19, 1978 - W. F. OWEN,* D. C. STUCKEV, J. B. HEALV, JR., L. Y. YOUNG and P. L. ... non-biodegradable, and also may contain materials ment processes ...
II al,'r Rt.war(h Vol. 13. pp. 485 to 4.92 ( P e r g a m o n Press Lid 1979 Printed in G r e a l Britain
IX)43-1354 7 t) 0601-(klgSS(12.00 1)
BIOASSAY F O R M O N I T O R I N G B I O C H E M I C A L METHANE POTENTIAL AND ANAEROBIC TOXICITY W. F. OWEN,* D. C. STUCKEV,J. B. HEALV, JR., L. Y. YOUNG and P. L. McCAgrV Department of Civil Engineering. Stanford University, Stanford, CA 94305, U.S.A. (Received in reri.~edform 19 December 1978) Abstract--Techniques are presented for measuring the biodegradability (Biochemical Methane Potential--BMP) and toxicity (Anaerobic Toxicity Assay--ATA) of material subjected to anaerobic treatment. These relatively simple bioassays can be conducted in most research laboratories without the need for sophisticated equipment. BMP is a measure of substrate biodegradability determined by monitoring cumulative methane production from a sample which is anaerobically incubated in a chemically defined medium. The ATA measures the adverse effect of a compound on the rate of the total gas production from an easily-utilized, methanogenic substrate. These techniques are demonstrated by an analysis • of the BMP and ATA of processed samples of peat. INTRODUCTION A simple and inexpensive procedure is needed to monitor relative biodegradability and possible toxicity of constituents in feed sources to anaerobic treatmerit processes. In order to satisfy these needs, a batch anaerobic bioassay technique was developed, The general procedure can be modified to estimate either the Biochemical Methane Potential (BMP) or to provide an anaerobic toxicity assay (ATA). For illustration, specially processed samples of peat were analyzed by these two procedures and the results are presented to demonstrate the usefulness of the techniques, BACgGnOUND Anaerobic treatment processes are widely used for biological stabilization of concentrated organic sludges. They provide a significant advantage over aerobic processes since they produce more energy in the form of methane gas than is required for operation. Because of dwindling reserves of fossil fuels, recent interest has grown in the potential of using anaerobic processes for converting organic residues into methane gas, an easily transported, clean-burning fuel. However, doubts have been cast on anaerobic treatment efficiency and process reliability since many potential residues for bioconversion are relatively non-biodegradable, and also may contain materials which are toxic to methanogenic micro-organisms. In the past, the cause of anaerobic system failures has been difficult to assess because of the complex mixtures being treated. Other difficulties include analysis for the great variety of potential inhibitors (many of which are not yet identified), and the lack of understanding of the interactions between inhibitors, other constituents in the digesting mixture, and the methanogenic bacteria. It has also been difficult to distinguish between failures due to toxic materials and those due to improper design or operation. • Present address: Culp/Wesner/Culp, P.O. Box 40, El Dorado Hills, CA 95630. 485
Bioassay techniques for measuring the presence or absence of inhibitory substances offer the most promise for resolving anaerobic treatment problems because they are relatively simple and inexpensive, and do not require knowledge of specific inhibitory substances. Also, bioassay techniques are essential for determining biodegradability since no chemical procedure is available which distinguishes between biodegradable and non-biodegradable organics. Both continuous (or semi-continuous) and batchfeed techniques have been used to evaluate toxicity and biodegradability. The continuous procedures closely simulate full-scale anaerobic operation; however, they are costly in terms of facilities, equipment, time, and personnel. Batch bioassay techniques do not have these limitations and thus permit the evaluation of a wide range of variables. Batch techniques can evaluate the influence of shock loads, but, in general, do not simulate the effects of real systems as well. However, they are still very useful for sorting out important variables and for the development of an efficient continuous-feed assay program. The Warburg respirometer has been widely used as a batch procedure to evaluate biodegradability and toxicity in aerobic systems. It has also been adapted for similar analyses with respect to anaerobic treatment processes (McCarty et al., 1963; Kugelman & McCarty, 1965 and Gossett & McCarty, 1976). However, the Warburg respirometer has sev.eral limitations: (1) it is costly and requires some degree of skill to operate, (2) a given instrument is limited in the number of samples that can be analyzed at one time, (3) sample size is limited, making subsequent analyses difficult, (4) it is difficult to sample the gas and liquid phases during the assay, and (5) extended incubation times are impractical and produce inconsistent results. In order to circumvent most of the above difficulties, the theory and procedures developed for the anaerobic Warburg were combined with serum-bottle' techniques for cultivation of anaerobes as described
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W.F. OWEN, D. C. STUCKEY,J. B. HEALY,L. Y. YOUNGand P. L. MCCARTY Table 1. Stock solutions for preparation of defined media Solution
Compound
Concentration (g J- 1)
SI
Sample
