Assessing the role of biochemical methane potential tests in determining anaerobic degradability rate and extent

Abstract

The biodegradability and bioavailability of hydrolysis-limited substrates under anaerobic (and aerobic) conditions can be represented by two key parameters--degradability (f(d)), or the percentage that can be effectively be destroyed during digestion, and first order hydrolysis coefficient (k(hyd)), or the speed at which material breaks down. Biochemical methane potential (BMP) testing uses a batch test (in triplicate), and by fitting against a first order model, can fit both parameters in the same test. BMP testing is now being widely used for anaerobic process feasibility and design purposes, and standardisation efforts are ongoing. In this paper, we address a number of key issues relating to the test method and its analysis. This includes proposal of a new fitting and parameter estimation method, evaluation of the impact of inoculum to substrate ratio on fitted parameters, and comparison to performance in continuous systems. The new parameter estimation technique provides an estimate of parameter uncertainty and correlation, and is clearly more suitable than model transformation and linear regression. An inoculum volume ratio of at least 50% (2:1 on VS basis) was required on a cellulose substrate to use methane production as primary indicator, as found by comparing methane production and solubilisation of cellulose. Finally, on a typical material, waste activated sludge, the batch test was slightly conservative in terms of degradability and rate, indicating a bias in the BMP test. The test is a cost-effective and capable method to evaluate potential substrates, but it should be noted that it is generally conservative, especially if sub-optimal inoculum is used.

Deterministic processes guide long-term synchronised population dynamics in replicate anaerobic digesters

“…This is the minimum retention time needed to prevent washout of slow-growing methanogens (Amani et al, 2010) and allows us to highlight differences in hydrolysis rate by running the process at an active point on the first order operating curve (Jensen et al, 2009; based on a cellulose hydrolysis rate of 0.2 per day; Jensen et al, 2011). The triplicate reactors were designated AD1, AD2 and AD3.…”

Anaerobic treatment of solid manure residues

“…A 95 % confidence interval in both parameters fd and B0, were estimated based on a two-tailed t-test (5 % significance threshold) with standard error determined using a Secant Fisher information matrix as per Jensen et al, (2011). Where relevant, errors were analytically propagated as described by Batstone (2013).…”

“…These additional tests were performed to assess suspected effects of chemical inhibitors and mass transfer limitations. These methods were adapted from Jensen et al (2011). Note that tCOD originally fed to the leachbed in Test 2, also included the COD contribution of added inoculum (leachate and solid digestate).…”

“…Tests were mixed by inverting once before every sampling event, but not between sampling events. Biogas volume was measured using a displacement manometer as described by Jensen et al (2011) and biogas composition determined as per Section 3.6. The batch experiments were terminated when the net methane produced was insignificant (<1% of the cumulative methane produced up to the last of those three days) (Holliger et al, 2016).…”

FNA-based pre-treatment of primary, secondary and digested sludge

“…BMP tests were employed to assess and compare methane production from different sludge sources with-and without pre-treatment (all tests were in triplicate), as described in Jensen et al (2011). To 160 mL serum bottles (100 mL working volume) the inoculum sludges and the substrate were added at a ratio of 1.5~2 (VS basis).…”