NOTICE: this is the author’s version of a work that was accepted for publication in Waste Management.  Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Waste Management, Vol.29(3), 2009, p.1218-1226. DOI: 10.1016/j.wasman.2008.08.024
1 REVIEW ARTICLE
2 TEST METHODS TO AID IN THE EVALUATION OF THE DIVERSION OF
3 BIODEGRADABLE MUNICIPAL WASTE (BMW) FROM LANDFILL
4
5 S.T. Wagland a, S.F. Tyrrel a*, A.R. Godley b and R. Smith c
6
7 a Centre for Resource Management & Efficiency, Sustainable Systems Department,
	8	School of Applied Sciences, Cranfield University, Cranfield, Bedfordshire, MK43 0AL,
9 UK
10
11 b WRc plc, Frankland Road, Blagrove, Swindon, Wiltshire, SN5 8YF, UK
12
13 c Richard Smith Consulting Ltd
14
	15	* Corresponding author. Tel.: +44 (0) 1234 750111 (ext 2717)
	16	E – mail address: s.tyrrel@cranfield.ac.uk
17
18
19
20
21
22
23

	1	Abstract
	2	A wide range of waste characterization methods are available, each developed for
	3	a specific purpose such as determining compost stability, or for landfill acceptance
	4	criteria. Here test methods have been evaluated for the purpose of assessing waste
5 treatment process performance and monitoring the diversion of biodegradable municipal
6 waste (BMW) from landfill. The suitability factors include the timescale of the method,
	7	applicability to a wide range of materials and ability to indicate the long-term
	8	biodegradability of organic waste samples.
	9	The anaerobic test methods, whilst producing reliable results, take at least several
	10	weeks to complete, therefore not allowing for regular routine analysis often required for
	11	diversion assessments. Short-term tests are required which can correlate with, and
12 therefore estimate, values obtained from long-term anaerobic methods. Aerobic test
13 methods were found to offer a significantly improved timescale compared with anaerobic
14 test methods; however they have limitations due to not measuring the full extent of
	15	sample biodegradability.
	16	No single test method was found to be completely sufficient for routine
	17	biodegradability analysis suitable for monitoring the BMW diversion from landfill.
	18	Potential areas for further research include spectrographic FT-IR or enzyme-based
19 approaches such as the ECD or EHT methods.
20
	21	Keywords- Biodegradability, waste characterization, waste treatment, landfill diversion,
22 organic waste
23

1	1. Introduction

	2	Tests used to estimate biodegradability are an important part of organic waste
	3	characterization since they can be used for assessing the biological stability of wastes
	4	(Adani et al., 2002; Iannotti et al., 1993) or for assessing the diversion of biodegradable
	5	waste from landfill (Godley et al., 2003). A wide range of biological and non-biological
	6	test methods are available. Biological test methods based on the use of aerobic
	7	respiration indices have been recently reviewed for assessing the bio-stability of organic
	8	waste and/or compost materials (Gomez et al., 2006). Suitability factors of the test
	9	methods include the timescale, applicability to a wide range of materials and ability to
	10	indicate the long-term biodegradability of organic waste samples.
	11	The basic principle of tests to estimate biodegradability is to assess how much of
12 the carbon can be mineralized and how quickly it will be degraded. The biodegradability
	13	tests can be used to assess the effectiveness of a certain treatment process. This is
	14	achieved by taking a representative sample of the waste before it goes through the
15 treatment process, and then taking another sample post-treatment (Environment Agency,
	16	2005). The degree to which the biodegradability of the waste is reduced indicates the
	17	effectiveness of the treatment process. Rapid and reliable methods are needed to allow
	18	for more frequent optimization of a treatment process (i.e. reduce the treatment time if
	19	applicable), offering financial benefits to the operator.
	20	Several countries have preferred methods of measuring biodegradability, however
	21	each biodegradability test method has been developed for a specific purpose e.g. compost
	22	stability. This review focuses on the applicability of each test method to assess treatment
23 process performance and aid in the quantitative evaluation of the diversion of BMW from

	1	landfill. A range of potentially applicable test methods are discussed, with suggestions
2 for further research and development being drawn from the overall conclusions.
3
4 2. Waste Biodegradability Test Methods
5
6 2.1. Anaerobic Test Methods
	7	Anaerobic test methods measure the biodegradability of a substrate under
	8	anaerobic methanogenic conditions. This particular type of method measures the release
	9	of ‘biogas’ (CO2 and CH4), typically using a digester sludge seed as a source of microbes
	10	(Godley et al., 2007). Under anaerobic conditions, in the absence of oxygen, organic
	11	materials decompose in the presence of methanogenic bacteria, which release carbon
12 dioxide and methane gas. This is shown in the following example for cellulose and
	13	hemicellulose respectively:
	14	(C6H10O5)n + nH24 + 3nCO2
	15	2(C5H8O4)n + 2nH24 + 5nCO2
16
	17	Anaerobic test methods, such as the generic biochemical methane potential
	18	(BMP), are bioassays in which a sample is incubated in a temperature controlled system,
	19	where the nutrients and bacteria are also added to allow optimized microbial
20 methanogenic conditions Such anaerobic methods describe the bioassay procedures, with
	21	variations in the methods including the nutrients added and the method of biogas
22 measurement. Table 1 provides a summary of the key aspects of a number of anaerobic

	1	test methods. Although other methods are available in the literature, these are only
	2	slightly different to those cited, and so they have not been included in this review.
	3	Whilst the recent studies into anaerobic test methods have focused on organic
	4	waste materials, some of the original methods were not prescribed for this material; for
5 example the blue book method for determining biodegradability of anaerobic sewage
	6	sludge (Standing Committee of Analysts, 1977). As the interest in the biodegradable
7 content of organic waste has increased, the anaerobic methods have been more widely
	8	applied to these materials.
	9	An early test method was described by Owen, Stuckey et al. (1979). This method
10 involved a simple glass set-up with an incubation temperature of 35°C (Owen et al.,
	11	1979). These tests were run for 30 days using samples of peat material. Although there
	12	was still activity remaining at the end of the tests, the majority of gas production occurred
	13	in the first 20 days.
	14	A test method used in a study by Shelton and Tiedje (1984) used a media which
	15	differed that used by Owen et al. The media used in the anaerobic tests is given in Table
	16	2. The duration of this test was 56 days. Rather than using organic waste materials, the
	17	et al., 1984).
	18	A test method of 60 days was used in an investigation by Pagga et al. (1993),
19 measuring chemical samples incubated at 35°C. Resazurin is used in the medium
	20	solution, however as an oxygen indicator (Owen et al., 1979; Pagga et al., 1993) and so is
	21	not used as a nutrient for methanogenic bacteria.
	22	A small scale anaerobic test method was used in a study to investigate the effects
	23	of lignin on the anaerobic decomposition of cellulose (Stinson et al., 1995). The mixture

	1	was incubated at 35°C for 2 months, and the released gas monitored using a syringe
2 system, and measured using gas chromatography (GC).
	3	A procedure modified from Stinson and Ham (1995) was applied more recently to
4 landfill samples (Kelly et al., 2006). Media was used modified from an earlier method
	5	(Shelton et al., 1984), and anaerobic sludge added (10%) as inoculum. The test bottles
6 were incubated at 35°C for 45 days, and the methane was measured using GC.
	7	The incubation test (GS90) is a test method 90 days in duration used in Austria,
8 using a moist fresh 1kg dry matter (DM) sample sieved to Ø 20 mm and saturated to
	9	water-holding capacity (Binner et al., 1999b). The sample is then incubated at 40°C
	10	under anaerobic conditions. Whilst 90 days is the preferred length of test, the test
	11	duration can vary e.g. 240 days, known as GS240.
	12	The fermentation test (GB21) method which is used in Germany uses a sample
	13	ground to <10 mm and filled to 300 ml with water (Bockreis et al., 2007). The Austria
14 version of the GB21 method measures a 50 g DM sample, sieved to Ø 20 mm and 200 ml
	15	of water is added (Binner et al., 1999b). Inoculum sludge (50 ml) is added, which in
	16	Austrian procedures is the leachate from the incubation test (GS90). This test can also
	17	vary in length (28 day test, GB28), although 21 days is the preferred length of time
	18	(Binner et al., 1999b).
	19	A small scale anaerobic test was used in a study by Harries et al. (2001). In the
	20	development of this method the seed is a laboratory maintained seed cultured over several
	21	years (Harries et al., 2001). Here the sample is incubated with the inoculum and the seed
	22	at 35°C for 30 days.

	1	For the BM100 method the waste sample is sorted and non-BMW components
	2	a removed, with the percentage BMW recorded. The biogas produced is collected in
	3	graduated measuring cylinder filled with water, which is displaced as the biogas enters
	4	the cylinder. The water is acidified to prevent dissolution of biogas (Environment
	5	Agency, 2005; Godley et al., 2007).
	6	Other examples of anaerobic biodegradability tests have been described in the
	7	literature (Bogner, 1990; Hansen et al., 2004; Zhang et al., 2007), however the variations
8 between these and those already described mostly involve the sample type and amount
	9	used, and for the overall purpose of this paper are not described.
10
11 2.2 Aerobic Respirometric Methods
	12	Aerobic respirometric methods are used to characterize organic waste samples by
13 measuring the oxygen (O2) consumption or carbon dioxide (CO2) production of a sample.
14 Biodegradable organic compounds are degraded under aerobic conditions as follows,
	15	using cellulose and hemicellulose respectively as an example:
	16	(C6H10O5)n + 6nO22O + 6nCO2
	17	(C5H8O4)n + 5nO22O + 5nCO2
18
	19	There are advantages and disadvantages of measuring either O2 consumption or
20 CO2 production. O2 consumption measurements are often favored since oxygen is
	21	directly responsible for the oxidation of organic matter (Gomez et al., 2005). Both
22 measurement methods require specific instrumentation, although CO2 measurements have
	23	been described as inexpensive (Adani et al., 2001) and less sophisticated (Gomez et al.,

1 2005) than O2 measurements. The calculation of O2 consumed from the CO2 produced
	2	assumes an O2:CO2 molar ratio of 1. In reality however, this ratio is dependent on the
	3	oxidation degree of the organic carbon (Adani et al., 2001; Gomez et al., 2005).
	4	The RQ values have been previously presented in studies of aerobic waste
	5	decomposition processes (Atkinson et al., 1997; Gea et al., 2004; Gea et al., 2007; Smars
	6	et al., 2001; Weppen, 2001). It was concluded from studies that RQ values are not
	7	suitable for indicating waste biodegradability or microbial activity (Gea et al., 2004;
	8	Genc et al., 2007). There is a wide range between these values, indicating that assuming
	9	an O2:CO2 molar ratio of 1 could be incorrect. This could lead to significant errors when
	10	CO2 measurements are utilized in respirometric test methods.
	11	There is a wide variety of respirometric methods; these can be classified as
	12	‘dynamic’ or ‘static’. Dynamic methods are those where the sample is aerated
	13	throughout the assay, which minimizes problems associated with O2 diffusion limitations
	14	(Gomez et al., 2006). In static methods, the samples are not aerated. The O2 transfer in a
	15	biological system is considered to be a limiting factor (Paletski et al., 1995), a major
16 disadvantage of static methods. Table 3 provides a summary of the key aspects of a
17 number of aerobic test methods.
	18	Oxygen Uptake is a static method developed by Iannotti et al (1993). The sample
19 was incubated for 16 h at 37°C, followed by a 1 h assay in which the decrease in oxygen
	20	level was monitored using a dissolved oxygen (DO) probe (Iannotti et al., 1993). This
	21	test was designed to assess the biological stability of compost.

	1	A dynamic test method used to assess compost stability has been described in
2 which microbial seed, nutrients and moisture were not added to the sample (Paletski et
	3	al., 1995).
	4	The American Society for Testing and Materials (ASTM) method is a dynamic
5 test used for determining the stability of compost by measuring oxygen uptake, with the
6 sample being incubated at 58°C for 4 days (ASTM, 1996).
	7	Specific Oxygen Uptake Rate (SOUR), like the O2 uptake test, was designed to
	8	assess the biological stability of compost. This is different from other respirometric tests
9 as the sample is suspended in water. Along with the SOUR test method, which is 5-6 h in
10 length, there is a cumulative oxygen uptake method (OD20) and SOUR in solid state
11 method (DSOUR). OD20 is the same as the SOUR method, except the duration is 20 h.
12 The DSOUR method is identical to the OD20 method, except no moisture is added to the
	13	sample (Lasaridi et al., 1998).
	14	The Dynamic Respiration Index (DRI) is a dynamic test method developed by
	15	Adani et al and designed to assess the degree of biological stability of waste derived
16 materials. There are three types of DRI reported; DRI, Real DRI (RDRI) and potential
	17	DRI (PDRI) (Adani et al., 2004). The moisture is adjusted to 750 g kg-1 for the DRI test
18 with optimal water content for PDRI and a lack of moisture adjustment for the RDRI
19 method.
	20	The Static Respiration Index (SRI) test is the same as the DRI described by Adani
	21	et al. except that it is a static test method (Adani et al., 2001).
	22	The Solvita compost maturity test is a commercially available static method. A
	23	compost sample of optimum water content is placed in the supplied test jar up to the fill

	1	level and the sample is allowed to ‘air’ for an hour without the lid in place. The jar is
	2	then sealed and the sample is left to equilibrate if necessary. Gel-paddles are then
	3	inserted into the test jar without them coming into contact with the compost. The test jar
	4	is kept at room temperature and out of direct sunlight for 4 h and the results are based on
	5	the color of the paddles (1-8 Solvita scale), indicating the CO2 concentration (Changa et
	6	al., 2003).
	7	Dynamic Respiration over 4 days (DR4) is a dynamic test method and is based on
8 the ASTM method, differing by using a smaller sample size and a lower temperature
	9	(Environment Agency, 2005; Godley et al., 2005). The samples are incubated at 37°C
10 for 4 days. This test method was developed to monitor the performance of a waste
	11	treatment process.
	12	Respiration Index (RI) is used to evaluate the stability of compost. There are two
	13	types of this static method, both described by Gomez et al. One is the RIT, which is
	14	incubated at the in situ (process) temperature recorded at the time of sampling. The other
	15	is RI37 which is incubated at 37°C
	16	The German Static Respiration Index (AT4 and AT7) methods last 4 and 7 days
17 respectively. The CO2 produced is measured as the CO2 is absorbed by NaOH, and the
18 pressure becomes negative, an oxygen generator produces O2 until normal pressure
19 conditions are restored. This set-up is commonly commercially known as the Sapromat
20 method; however alternatives such as the Oxitop method exist. The O2 production is then
	21	recorded. Similarly to the DR4 test method, these tests were developed to describe
	22	biological activity of waste with respect to landfill regulations.

	1	In common with anaerobic test methods, main differences in aerobic methods are
2 the amount of sample used, test conditions and test duration. A multitude of test methods
	3	have emerged in recent years as researchers have adapted previous methods to suit the
	4	practical needs of their studies, resulting in a modified method, which varies only slightly
	5	from other existing aerobic methods.
6
7 2.3 Temperature In crease Methods
	8	In addition to the aerobic respirometric methods, there is also the Dewar self‑
	9	heating test, which measures the heat produced by the sample under aerobic conditions,
10 rather than the gases consumed or produced. The self-heating tests have been
	11	investigated for the indirect estimation of respirometric activity (Koenig et al., 2000) and
12 maturity of compost material (Weppen, 2002).
	13	The self-heating test is useful as it is very simple to operate, measuring the
	14	temperature increase due to sample activity.
15
16 2.4 Spectrographic Methods
	17	Fourier Transform Infrared Spectroscopy (FT-IR) is a technique that is efficient in
18 providing comprehensive information on chemical composition of heterogeneous
	19	materials. FT-IR characterizes the classes of chemical functional groups present in a
20 sample (Chen, 2003), enabling the analysis of a complex mixture of chemicals found in
	21	waste materials. The technique has been applied to landfilled MSW during in-situ
	22	aeration (Tesar et al., 2006), during composting (Castaldi et al., 2005; Smidt et al., 2005)
	23	and anaerobic digestion (Smidt et al., 2007a).

	1	The absorbance observed in the FT-IR spectra, along with the bands present is
2 indicative of sample maturity. For example aliphatic methylene bands are weaker in
	3	landfill samples than in MBT waste material whilst a band assigned to aromatic amines is
	4	not observed in landfill samples, since these compounds decrease during biological
	5	treatment (Smidt et al., 2007b).
6
7 2.6 Enzymatic Test Methods
	8	Biodegradation of organic materials is a process performed by fungi and bacterial
	9	organisms, and as such the mineralization of the organic matter is through the action of
	10	extracellular enzymes (Pelaez et al., 2004). A more extensive and comprehensive
	11	enzyme system is required as the substrate material becomes more complex (Tuomela et
	12	al., 2000). The quantification of the activities of a range of enzymes within a waste
	13	material has been investigated as a means of assessing compost quality and maturity
	14	(Cayuela et al., 2008; Mondini et al., 2004; Pelaez et al., 2004; Tiquia, 2005). The
16	phosphatase and dehydrogenase, all of which are associated with the decomposition of
17		the respective substrates found in waste material throughout composting.
18		The enzymatic cellulose degradation (ECD) method is a novel enzymatic
19		approach to biodegradability measurement (Rodriguez et al., 2005). A mixture of
20		cellulase and xylanase (hemicellulase) enzymes were used in this study, which studied
21		samples taken from a landfill site. The samples were mixed with a phosphate buffer (pH
22		5.5) at 40°C, and the monosaccharides liberated were recorded after the incubation period
23		(40 h). The mass of the monosaccharides that are released by the MSW samples is

	1	reported to the initial mass of sample hydrolyzed in order to assess the biodegradability
	2	of waste samples.
	3	An enzymatic approach based on the ECD method has been developed and
4 applied to a wide range of organic waste materials including untreated and treated MSW
5 derived BMW, food, wood and garden wastes (Wagland et al., 2008; Wagland et al.,
	6	2007). The enzymatic hydrolysis test (EHT) uses a mixture of crude cellulase and
	7	hemicellulase enzymes (which also exhibit protease activities). The samples are mixed
	8	with a phosphate buffer at pH 4.75 and autoclaved to sterilize the mixture. The dissolved
9 organic carbon (DOC) is measured and a prepared enzyme mixture added. The mixture
10 is incubated at 50°C for 20 h, and the DOC is measured. The DOC released from
	11	autoclave is deducted from the final value to provide an indication of sample
	12	biodegradability.
13
	14	3. Discussion
15
16 3.1 Method Practicality
	17	The focus of this review is to assess the suitability of each method for the purpose
18 of monitoring waste treatment process performance and the diversion of BMW from
	19	landfill. Here each method is critically discussed regarding sample size used (and hence
	20	the representation of overall waste material), timescale, reliability and applicability to a
	21	wide range of heterogeneous waste materials.
22
	23	3.1.1 Anaerobic Tests

	1	Several of the anaerobic methods (Owen et al, Pagga and Beimborn and Harries et
	2	al) are small scale tests. These tests use samples that are comparatively small in relation
3 to the sample size of the GS90 test (1 kg DS) and the GB21 method (50 g DS). In
	4	general the larger the sample, the better representation that sample is of the overall waste
	5	batch. For example if a waste batch contained 10% cardboard, then this ideally needs to
	6	be reflected in a sample used in a test, and using 0.5 g of a sample (as with the Harries et
	7	al method) is unlikely to show a consistent 10% cardboard composition, and hence offer
	8	a reasonable representation of the waste. Shelton and Tiedje also used relatively small
	9	samples (50 µg/ml), although these were chemical samples. Considering other larger
	10	scale tests available, these small scale tests are less suitable for the monitoring of mixed
	11	solid waste. The larger scale test methods use sample sizes more representative of the
	12	waste material, and so provide more reliable and valid data.
	13	The method of measuring biogas production varies between the methods. The use
	14	of syringes (Owen et al, Harries et al) should be restricted to smaller scale tests, as the
	15	size of syringe required for a larger sample (and therefore larger quantities of biogas
16 produced) would be impractical. Alternatively, the syringes could be emptied on a more
17 regular basis, but this could increase the measurement error. The BM100 method
18 requires a 20 g LOI sample, which can produce as much as 15 liters of biogas over the
	19	100 day period (Godley et al., 2007). This would be difficult to accurately capture in
20 syringes. The GB21 method requires a 50 g DS sample, however biogas is only
	21	measured for 21 days, and so the biogas produced is unlikely to exceed 15 liters.
	22	Reported results include 10 liters of biogas released at 21 days (Bockreis et al., 2007).
	23	The GS90 test method requires 1 kg DS so the expected biogas production is

	1	considerable. Measurements by Eudiometer (GS90) or by acidified water-filled cylinders
	2	(BM100) are therefore much more suited for the larger scale tests that are required for
	3	characterizing samples that are of a more representative size. The method for biogas
4 production measurement has been previously discussed (Anaerobic Biodegradation
5 Activity and Inhibition (ABAI) Task Group, 2006). Manometric and volumetric
6 measurements were found to have limitations. There is a limited range of accuracy
	7	associated with manometric analysis, whilst due to changes to the atmospheric pressure
	8	and evaporation of water in volumetric systems can cause inaccuracies (Anaerobic
9 Biodegradation Activity and Inhibition (ABAI) Task Group, 2006).
	10	It has therefore been recommended that gas analysis is performed using GC
	11	instead of volumetric gas release (Anaerobic Biodegradation Activity and Inhibition
12 (ABAI) Task Group, 2006), as used in studies such as Stinson and Ham (1995) and Kelly
	13	et al (2006). This technique would provide more accurate data for methane and carbon
14 dioxide production; however this technique is more expensive than the other methods of
15 gas production measurement.
	16	Under anaerobic conditions, microbial growth efficiency is lower than in aerobic
	17	conditions. As a result the biogas release is an accurate representation of the microbial
	18	activity since a very small amount of the mineralized organic carbon is converted to new
	19	biomass. This is a major advantage of the anaerobic test methods. In aerobic conditions,
20 the microbial growth efficiency is much higher, and so more of the mineralized organic
	21	carbon is converted to microbial biomass and therefore the carbon dioxide released is not
	22	an accurate representation of the organic carbon mineralization.

	1	The major disadvantage of the larger scale anaerobic tests (GB2 1, GS90 and
	2	BM100) is that whilst the results produced are reliable, the time scale for each test is not
	3	practical for routine analysis. Test durations of 21, 90 or 100 days have financial and
	4	operational implications for waste treatment and landfill operators if biodegradability
	5	data is delayed.
6
7 3.1.2 Aerobic Tests
	8	The aerobic ASTM method operates at 58°C. This higher temperature could
	9	present some disadvantages for such a test method since the solubility of oxygen in water
	10	decreases with an increase in temperature. This may limit the oxygen transfer in the
	11	waste material which could result in lower results than expected. So whilst the high
	12	temperature may accelerate some reactions the biological activity will be hindered.
	13	The static respiration methods generally give lower results that dynamic tests
	14	(Godley et al., 2005), which indicates the advantage of aeration throughout the test
	15	duration.
	16	The SOUR method uses a 3-8 g sample. This is a small sample, and so may not be
	17	a very good representation of the sample as a whole, thus reducing the reproducibility of
	18	the test. However, the aqueous suspension used in the method offers several advantages.
	19	One major advantage is that there is not a gas-liquid barrier on the surface of the substrate
	20	(Lasaridi et al., 1998). This means that gaseous exchange can occur immediately due to
	21	the direct contact between the substrate material and the microbes, maximizing the
22 diffusion of oxygen.

	1	The minimization of diffusion rates is important since limited oxygen transfer
	2	through biomass layers into bacterial cells is typically considered to be the rate-limiting
	3	step (Adani et al., 2004; Paletski et al., 1995).
	4	Compositional methods such as dry matter or solids (DM or DS respectively) and
	5	loss-on-ignition or volatile solids (LOI or VS respectively) do not describe the
6 biodegradability of a sample material. The LOI and VS analyses indicate organic carbon
	7	content, but not biodegradable carbon content. Not all carbon is amenable to
8 biodegradation, and so the use of carbon content to indicate biodegradability, or BMW
	9	diversion from landfill, would result in an over-estimation of sample biodegradability.
	10	Certain methods such as the aerobic AT4 or anaerobic GB21 methods use the DS
	11	content (mg O2/g DS or mg/kg DS respectively). Considering the DS content, this would
	12	include the inorganic material, which is non-biodegradable, meaning that data presented
	13	in this form may not be comparable. Alternatively using LOI or VS only takes the
	14	organic fraction into account, which would allow for the varying inorganic content,
	15	allowing valid comparison between samples.
16
	17	3.1.3 Alternative Tests
	18	Temperature increase methods may not be suitable since temperature increase is
	19	due to chemical and biological reactions within the sample. Not all these exothermic
	20	reactions are related to the respiration reactions, such as acid hydrolysis. Some of the
	21	heat increase, to a certain degree, will not be respirometric activity. The results are
	22	therefore unlikely to be accurate, considering that the moisture content of the sample will
	23	also affect the heating. Precise determination of bioactivity using the Dewar self-heating

	1	test is difficult under any condition, and additional factors such as packing density and
	2	humidity require careful consideration. The applicability of the Dewar self-heating test to
	3	fresh MSW samples has not been investigated to the authors’ knowledge, and as such this
4 may indicate that other methods may offer more suitable options.
	5	Spectrographic techniques such as FT-IR have been shown to be efficient at
	6	assessing the chemical properties of waste material, indicating sample stability. However
7 no research has indicated that this technique can quantify the amount of biodegradable
	8	material removed. This technique could be used in compost quality, or landfill
	9	acceptance criteria, based on the presence of certain bands indicating waste composition
	10	and whether the sample is stable or not. Aerobic and anaerobic test methods enable a
	11	simple calculation of biodegradability reduction from a waste treatment process, and so
12 for the purpose of monitoring BMW diversion from landfill, FT-IR is perhaps not
	13	suitable, however further research could enable this technique to become suitable.
	14	Measuring the enzymatic activity present in a waste material has been shown to
	15	be a suitable method for the characterization of compost stability (Cayuela et al., 2008).
	16	The enzyme activity of the stabilized compost material varied depending on the starting
	17	substrate (Mondini et al., 2004). There is a necessity to perform several measurements to
	18	understand the activities of the wide range of enzymes, which is a disadvantage of this
	19	approach. Whilst measuring the enzyme activities may offer a good indication of
20 compost maturity, this approach has not been applied to fresh MSW input samples, and
	21	the significantly different substrates available in fresh and treated waste samples would
22 require a complex and possibly an individual analytical approach to each material. This

	1	would not allow simple and rapid monitoring of waste treatment processes, and so is
2 unsuitable for the monitoring of BMW diversion from landfill.
3
4 3.2 Correlations with Anaerobic Methods
	5	Assessing the complete biodegradability of the sample is ideal; however short‑
	6	term tests cannot provide this and so are used to correlate with anaerobic tests. This
	7	allows for the prediction of long-term biodegradation potential in a shorter length of time,
	8	depending on a strong correlation of the tests. A summary of correlation coefficients
	9	from the evaluated studies is shown in Table 4.
	10	The German SRI (AT4 and AT7) tests have been investigated, along with an
	11	AT10 test (Binner et al., 1999a; Binner et al., 1999b). It was found that the AT10 results
12 did not produce enough additional information to make the test more practical than the
13 AT7 test, and as a result the AT7 test is recommended. The AT7 shows a strong
	14	correlation with the anaerobic incubation test (GS90) with correlation coefficients (r) of
	15	0.88-0.906 (Binner et al., 1 999b). This relationship indicates that as the results of the
	16	AT7 increase, the results obtained from the GS90 are also expected to increase.
	17	For routine testing, the length of the aerobic tests may still be too long, not
	18	providing results quickly enough and having financial implications for the treatment
	19	process operator.
	20	The ECD method was shown to correlate with a classical BMP test, with
	21	correlation coefficients (r2) between 0.65 and 0.87 (Rodriguez et al., 2005). This
	22	relationship shows that as the ECD results increase, the expected BMP results will also
	23	increase (i.e. low biodegradable substrate gives low ECD and BMP values).

	1	However, this method has the limitation that only the monosaccharides are
	2	measured. Cellulose can be hydrolyzed into cellodextrins and cellobiose molecules before
	3	glucose molecules are produced. As a result, the measurement of monosaccharides may
	4	not reveal the full extent of the cellulose hydrolysis. Organic waste material will also
	5	contain other enzyme hydrolysable substrates, such as proteins, and these may require
	6	further consideration.
	7	A relationship was observed for the EHT with the BM100 with a correlation
	8	coefficient (r2) of 0.59. This method indicates the availability of enzyme hydrolysable
	9	substrates such as proteins (unlike the ECD). However this method has the limitation of
10 potentially excluding biodegradable DOC released in the autoclave procedure (Wagland
	11	et al., 2008). The carbon released in the autoclave procedure would contain
12 biodegradable and non-biodegradable carbon, and therefore careful consideration and
	13	further development is required.
	14	The DR4 test correlates with the BM100 test method, allowing the estimation of
	15	BM100 data from DR4. A shorter anaerobic test, GS21 (fermentation test), also
	16	correlates well with the Austrian GS90 test (Binner et al., 1 999a). The AT4 is the
17 recommended test method in Germany and Austria, with the allocated landfill acceptance
	18	criteria of 5 mg/g DM and 7 mg/g DM respectively (Muller et al., 2005). The correlation
19 of the DR4 method with BM100 data has been reported (Godley et al., 2007), whilst the
20 correlation of the AT4 method with the GB21 method has also been investigated (Cossu
	21	et al., 2008). The aerobic test methods have disadvantages such as the microbial growth
	22	efficiency, in which new biomass is produced efficiently from the digestion of the waste
	23	material, and so the carbon dioxide produced doesn’t sufficiently represent the degree of

	1	biodegradability. Aerobic test methods also have the disadvantage of measuring only the
	2	initial rate of biodegradability due to these tests measuring the readily biodegradable
	3	materials. The length of aerobic tests does not allow the measurement of slowly
4 biodegradable material. Anaerobic test methods, such as the BM100 and GS90, give
	5	a reliable results and measure the extent of biodegradability as the length of these tests is
	6	clear disadvantage, but allows for the degradation of readily biodegradable and slowly
	7	biodegradable materials.
8
9 4. Conclusion
	10	Biodegradability testing is an important part of monitoring BMW diversion from
	11	landfill in the EU. Data obtained from these tests assist the waste treatment operators in
	12	optimizing the waste treatment process and in the UK provide local authorities with
	13	information with which to calculate BMW diversion. Therefore there is a need for a
	14	rapid and cost-effective test method that would correlate with the reliable BM100 test
	15	method, which is not suitable for regular routine testing due to the duration.
	16	The current biodegradability test methods have limitations, and no one test
	17	method is currently sufficient for routine biodegradability assessment. Further research is
	18	needed to develop the alternative and rapid test method that is required. From this review
	19	potential areas for further research include spectrographic FT-IR or enzyme-based
20 approaches such as the ECD or EHT methods.
21
22 Acknowledgements
	23	This research is part of a wider programme of research on waste characterisation

	1	sponsored by the Department for Environment, Food and Rural Affairs (Defra), from
2 whom the authors are grateful for permission to publish. Views expressed are those of the
	3	authors’ alone.
	4	The authors would also like to thank Dr M. W. Milke for the invaluable feedback
	5	provided.
6
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32

Wagland et al. Table 1

Method	Temp/
°C	Length of Test	Moisture	
Owen et al.	35	30 days. Majority of
gas production in
first20 days,	No Moisture
Adjustment	
Shelton and		however still activity
after 30 days	Chemical
compounds
used,	
	35	8 weeks		
Tiedje			therefore no	
Pagga and			moisture
adjustment
No moisture	
	35	60 days		
Beimborn			adjustment	
Stinson and			No moisture	
	35	60 days		
Ham			adjustment	
Kelly et al.
Incubation test	35	45 days	No moisture
adjustment
Saturated to	
	40	90 days	water holding	
GS90			capacity	
Fermentation
test	35	21 days	50 gDS
sample + 300
mL H2O	
GB21			(200 mL in	
Harries, Cross		3 months, some	Austria)
Oven dried at	
	35	samples produced all		
and Smith			105°C	
BM100	35	gas within 2 months
Upto 100 days	Dried at 70°C
to a DM	
		(possibly longer)	content of 87‑
93%	

Seed

Mesophilic (35°C) 

digested sludge

Sewage sludge
from municipal
digesters sparged
with 10% CO2
90% N2

1-3 g/LTS
digested sludge

10% digested sludge solution prepared with
inoculum

Sludge from
anaerobic digester

10% by volume
inoculum

No seed

Sample is fresh
and moist

Anaerobic
digested sludge

Laboratory
maintained seed
‘cultured’ over
several years,
regularly fed with
medium.

Anaerobic
digested sludge
(3 gin50 mL-6%
by DM)

References

(Owen, Stuckey et
al., 1979)

(Shelton and Tiedje,
1984)

(Pagga and
Beimborn, 1993)

(Stinson and Ham,
1995)

NI /kg DS

mg/kgDS

NI /kg DS

(Harries, Cross et al.,
2001)

NI /kg LOI

l/kg LOI

Reporting Units

m3 CH4/kg COD
m3CH4/kgTS
Net gas production

(mL)

Percentage of theoretical gas production (%)

Total percentage of biodegradation, DT (%)

Rate of cellulose
decomposition
calculated

Milliliters of methane	(Kelly, Shearer et al.,
per gram of dry MSW	2006) (mL/g)

(Binner and Zach,
1999)

(Binner and Zach, 1999; Bockreis, Muller et al., 2007)

Cumulative gas production (mL)

BMP value
(m3 CH4/tonne DM)

(Godley, Lewin et
al., 2007)

Sample Size	Sample Preparation	Biogas Measurement
Method	
Peat samples
<2 g/L
degradable
COD content	30% CO2 70%N2 passed
through at flow rate of
0.5 L/min for 15 min	Glass syringes equipped with 20
gauge needles	
	Not waste samples, therefore	UniMeasure pressure transducer	
	no preparation	equipped with a P-8 bellows	
100 mg/l C	Sparged with nitrogen.		
(20 mg/L if		Pressure measurement (mbar)	
sample is toxic)	Adjusted to pH7		
0.05 g non‑			
lignin substrate	Dried and screened to 2 mm		
		Gas samples collected from bottles	
(mass of			
		following incubation measured using	
sample = 0.05	Purged with N2 gas to remove		
		gas chromatography	
g/ (1- lignin	O2		
fraction)			
		Gas samples taken at end of	
2 g MSW			
	Dried and shredded <10mm	incubation period were analyzed	
sample			
		using gas chromatography	
		Pressure measurement by	
		‘Eudiometer’	
1 kg DM plus			
	Sieved to <20mm		
water			
		Gas generation calculated to normal	
		conditions (0°C, 1013 mbar)	
		Gas production presses NaOH	
	Ground to <10mm		
50 gDS		solution into a graduated measuring	
	(<20mm in Austria)		
		cylinder	

Syringe via 3-way valve connected
to a manometer. Syringe draws out
gas until normal barometric pressure
is reached

0.5 g

Dried at 105°C, grinded and
sieved to <1 mm

20	LOI
g			
	Non-BMW components		
	removed, and percentage	Biogas is collected in a graduated	
200 mL			
	BMW recorded. Reaction	measuring cylinder filled with	
medium			
	mixture sparged with	acidified water	
	nitrogen		
50 mL seed			

Table 1. Anaerobic test methods summary

Method	Medium/ Inoculum	References

Owen et
al.
Shelton and Tiedje
Pagga
and
Beimborn
Harries,
Cross and
Smith
Godley et
al.

Resazurin
KCl
Na2MoO4.2H2O
Folic acid
Pantothenic acid
Phosphate Buffer
KH2PO4 K2HPO4
Resazurin
KH2PO4
Na2HPO4. 12H2
O
NH4Cl
Resazurin NH4Cl
KH2PO4.3H2O
NaH2PO4 NaHCO3

KH2PO4 NH4Cl
CaCl2.2H2O
MgCl2.6H2O or MgSO4.7H2O

MgCl2.6H2O

(NH4)2HPO4
MnCl2.4H2O
ZnCl2
Pyridine
hydrochloride
B12
Mineral Salts
NH4Cl
CaCl2.2H2O
MgCl2.6H2O
FeCl2.4H2O
CaCl2.2H2O MgCl2.6H2O

FeCl2.4H2O Tryptose
Yeast extract
H2O
FeS/CaCl2
Mercapto-ethane sulphonic acid
(MES)

FeCl2.4H2O Na2S.9H2O

CaCl2.2H2O CoCl2.6H2O FeCl2.4H2O
Riboflavin
acid
Trace Metals
MnCl2.4H2O
H3BO3
ZnCl2
CuCl2
Trace Elements MnCl2.4H2O
H3BO3 ZnCl2
Trace Elements
FeCl3.6H2O
CoCl2.6H2O MnCl2.4H2O

NH4Cl
H3BO3
Na2S.9H2O
Thiamin
Thioctic acid
Na2MoO4.2H2
O
CoCl2.6H2O
NiCl2.6H2O
Na2SeO3
CuCl2
CoCl2.6H2O
NiCl2.6H2O
Na2SeO3
Trace Elements
AlCl3.6H2O
CoCl2.6H2O CuCl2.2H2O
H3BO3
MnCl2.4H2O
ZnCl2
NiCl2
Na2MoO4.2H2
O
CuCl2.2H2O

MgCl2.6H2O
CuCl2.2H2O
Biotin
Nicotinic acid
After Cooling
NaHCO3 Na2S.9H2O
Na2MoO4.2H2O
Na2SeO3.5H2O
Na2WO4.2H2O
(NH4)6Mo7O24.4H2
O
NiCl2.6H2O
ZnCl2

(Owen et al.,
1979)
(Shelton et al.,
1984)
(Pagga et al.,
1993)

Na2 WO4.2H2O	(Environment Agency, 2005)

(Harries et al.,
2001)

Table 2. Media used in the anaerobic test methods

Wagland et al. Table 3

Reporting Units

Test Purpose/
	Common Use	 Compost stability, degree to which the biodegradable

mg O2/g VS/h	fraction in solid wastes has been diminished during composting Compost stability/
mg O2/h/g DS	performance of composting process

Method	Abbreviation	Dynamic Inoculum/ /Static	Seed	Nutrients	Moisture	Temp/°C Length of Test	Sample Prep	 Samples sieved	

References
(Iannotti, Pang et al., 1993)
(Paletski and Young, 1995)
(ASTM, 1996)
(Lasaridi and Stentiford,
1998)
(Lasaridi and Stentiford,
1998)
(Iannotti, Pang etal., 1993; Lasaridi and Stentiford,
1998)
(Adani, Confalonieri et al., 2004; Adani, Lozzi et al., 2001)
(Adani, Lozzi et al., 2001)
(Adani, Lozzi et al., 2001)
(Adani, Lozzi et al., 2001)
(Changa, Wang et al., 2003)

Sample Size

Solvita ®
maturity scale
(1-8, with 1
being very	Compost maturity active, and 8
being very
mature)

Compost stability/ extent to which
mg O2/g VS/h	readily biodegradable material has decomposed.

mg O2kg-1VS h-1

mg O2kg-1VS h-1

Compost stability

Degree of biological stability

mg O/kg LOI

Evaluation of
mg O2 gOM-1h-1	composting process/ stability of compost

mg O2/g DS

Monitoring performance of MBT and other treatment processes

Describe the biological activity of waste with respect to landfill regulations.

(Godley, Muller et al., 2005)
(Gomez, Vazquez Lima et al., 2005) (Gomez, Vazquez Lima et al., 2005)
(Binner and Zach, 1999a; Binner and Zach, 1999b)

							16h	(<9.5mm) to		
Oxygen Uptake	O2 Uptake	Static	None	None	50-55% w/w	37	incubation	remove glass,	60 g dry	
							1 h assay	plastics, inerts	weight	
								and oversized		
								materials		
								Compost	20 g wet	
Paletski and Young	N/A	Dynamic	None	None	None	35	48 h			
								Samples	weight	
American Society				Nitrogen						
for Testing and	ASTM	Dynamic	Mature	and	50%	58	4 days		500g	
Materials			Compost	Phosphor						
Specific Oxygen										
	SOUR				Suspension		5-6h			
Uptake Rate										
				Phosphate					3-8gwet	
Cumulative Oxygen	OD20			Buffer,	Suspension		20h	Composts	weight	
Uptake- 20h		Static	None	CaCl2,		30		Sample	(dependant	
				FeCl3 and					on activity of	
Specific Oxygen				MgSO4				<9.5mm	sample)	
Uptake Rate in Solid	DSOUR				None added		20h			
State										
							Maximum			
Dynamic Respiration	DRI				750 gkg-1		oxygen uptake			
Index							over 24 h			
									20-40 kg	
Real Dynamic		Dynamic	None	None		Process		Shredded	depending	
Respiration Index	RDRI				None added		As DRI	<50mm	on bulk	
									density w/w	
Potential Dynamic					Optimal Water			Quartered		
	PDRI						As DRI		samples used	
Respiration Index					Content					
							Maximum			
Static Respiration	SRI	Static	None	None	750 gkg-1	Process	oxygen uptake			
Index							over 24 h			
								Removal of		
						Room	4 h (+ 48 h	stones and		
Solvita ® Compost					Optimum/		before to		To fill line of	
Maturity Test	Solvita ®	Static	None	None	saturation	Temp (20-	equilibrate if	large stems	test jar	
						25)	necessary)	and wood
chips		
								Non-BMW		
								removed and		
				Phosphor				% BMW		
Dynamic Respiration
over 4 Days	DR4	Dynamic	Mature
Compost	and	50%w/w	37	4 days	recorded.	200-250 g
DM	
				Nitrogen						
								Large BMW		
								shredded		
								Samples		
Respiration Index at	RIT					Process	4 h incubation	sieved		
Process Temperature							90 min assay	(<10mm) to	250 ml	
		Static	None	None	40-50%w/w		18 h	remove glass,	(weight	
Respiration Index at	RI37					37	incubation	plastics and	recorded)	
37°C							90 min assay	other inerts		
German Static										
	AT4									
Respiration Index	(Sapromat E)						4 days		30-40 g of	
over 4 days					Saturation					
German Static		Static	None	None	(~40-50%)	20		<20mm	wetted	
	AT7								sample	
Respiration Index
over 7 days	(Sapromat E)						7 days			

Short-term Long-term	Correlation
Method	Sample	coefficient (R2)	Reference Method
		MSW excavated from	0.80		
AT4	GB21	closed landfill (3 sites)		(Cossu et al.,	
				2008)	
		Pre-treated residual waste	0.60		
AT7	GS90	Pre-treated residual waste	0.83	(Binner et al.,	
				1 999b)	
GB21	GS90	Pre-treated residual waste	0.95	(Binner et al.,	
				1 999b)	
DR4	BM100	MSW derived BMW	0.54	(Godley et al.,	
				2007)	
			0.65		
ECD	BMP	MSW extracted from
landfill (3 sites)	0.79	(Rodriguez et
al., 2005)	
			0.87		
EHT	BM100	MSW derived BMW and	0.59	(Wagland et al.,	
		specific waste materials		2008)	

Table 4. Summary of correlation coefficients between short-term and long-term biodegradability test methods.