Categoría II: Autoridad

William F. Brinton 1 _{P. Storms}1_{, E. Evans}1_{, A. Underwood}1_{, T.C. Blewett}2

Key words: USA compost hygiene maturity E. coli

Abstract

Landfill diversion by composting of “green” wastes including grass and food has enabled states to achieve mandated recycling goals. In America, standards for quality and hygiene for intensive and organic agriculture use of non-sludge composts are still under development and 47% of states do not specify any tests. We evaluated 94 biocomposts from facilities processing 2.2 million-m3 a-1 green waste. Only 20% gave cress-yield ≥ 80%. Only two composts contained Salmonella but 37% exceeded combined pathogen expectations. Faecal coliform correlated closely with E. coli levels and 3 samples had detectable E. coli-0157-H7. Processing size of facilities had a negative correlation to hygiene quality and windrow methods had best results.

Introduction

Composting in the United States is a strategy to reduce landfilling of organic wastes while it originated in organic farming (Heckman, 2006). Large scale composting was first attempted in the 1950’s for municipal solid waste (MSW) with poor results due to contamination. New growth in the industry came about in Europe and N. America with legislated recycling mandates for bulky woody yard “green” waste, following improved understanding of source separation. Never the less, in the USA only 22 states have imposed restrictions on yard trimmings in landfills and only half have published test guidelines independent of sludge composting. This study assesses quality of for agricultural utilization. Composting is widely assumed to have no significant risk to society but few comprehensive studies have been conducted. In the 1960’s the US EPA examined thermal inactivation of pathogens and stability factors in sludge composts and the results became regulatory as the EPA-503 rule, now widely applied to all types of green composts (Brinton, 2004).

The EPA503 law assumes hygiene of sludge is inferred by using faecal coliform as a surrogate indicator for Salmonella (Yanko, 1988). Early correlations from 260 sludge-composts indicated pathogenic Salmonella was low if faecal coliform counts were below 1,000 MPN g-1 TS and oxygen consumption had declined. However, these excellent early efforts predated the rise of toxigenic E. coli

now virtually endemic in manures and found in the food chain with potentially deadly results. With greater quantities and types of ROM used in intensive growing, using a Salmonella surrogate model to examine hygiene is not appropriate, as green waste now contains significant E. coli (Doyle). With the increased compost use in horticulture, stability and salinity tests relevant to buyers and not unduly influenced by waste-industry organizations, must be developed. The reasons for this study were: increased use of compost in horticulture (Blewett, 2005), availability of updated EPA microbiological methods and new evidence that direct E. coli tests are more suited for hygiene tests (Doyle, 2006), evidence that unstable, immature composts permit pathogen regrowth resulting in increased incidence of E. coli entering the food chain (Ingram, 2007), and harmful plant effects of unstable composts used for container plants (Brinton, 2004). Phytotoxins in compost are similar to extracellular bacterial toxins resulting from incomplete microbial oxidation of ammonia from too high temperature and imbalanced pH conditions, with episodic accumulation of short-chain fatty acids from incomplete oxidation under oxygen stress especially if food scraps are composted in any quantity.

We examine quality and hygiene of non-sludge composts made in three states (WA, OR, CA) where statutory landfill diversion is practiced and two states have compost test requirements. In WA, organic wastes are classified by feedstock type, and large facilities with yard waste and food waste must perform at least one test per year for faecal coliform and salmonella. In OR, only non-green facilities are regulated at all. In CA, Salmonella and faecal coliform tests must be recorded annually and up to 2,000 m3 of compost may be sold without regulation. Principle markets are bulk use for soil replacement with increasing uses in agriculture (Blewett, 2005). Therefore, understanding quality of material is important for agricultural and horticultural safety and success.

Materials and methods

1 _{Woods End Laboratories, Mt Vernon MAINE USA, E-Mail [email protected], Internet www.woodsend.org} 2 _{DOW Agro-Sciences LLC Indianapolis Indiana USA}

Trained professionals conducted sampling over 2 yr on-site at 94 compost facilities by permission and only for market-ready product. Samples were brought chilled to a laboratory in 24h. We examined bacteria according to updated EPA and ÖNORM protocol, TN by combustion, C by LOI@550ºC÷2, TS by 70ºC drying @ 24h, salinity as conductivity by saturated paste extract, Solvita® after Woods End, Cress after BGK, industrial contaminants PAH and phthalates by solvent extract with LC/MS or GC/MS/MS. Some sites were re-sampled for bacteria tests after 3 and 12-weeks.

Results

Salinity of composts ranged hugely from 0.4 to 24 dS m-1 as did cress growth (corrected for salinity) of 16 to 160% (Tab. 1). Composts were only moderately mature (mean C:N = 23; mean Solvita = 6.2; mean NO3:NH4 ratio 0.3) indicative of incomplete curing. We observed a statistically significant

relationship of faecal coliform and E. coli bacteria for 55 paired samples (r2= 0.85, p<0.0001) suggesting validity of faecal coliform tests as a generic pathogen indicator. There was no correlation of faecal to Salmonella, the latter found in only 2 facilities at low levels (<3 MPN/4g) as expected. Presence/absence of allowed manure in green composting also had no statistical relationship to hygiene quality. Three samples were positive for E.coli-0157:H7 confirmed with duplicate retesting. The highest amount f samples exceeding EPA-503 rule was observed in OR, followed by WA then CA (Tab. 1). Overall size had a significant impact; for facilities handling less than 45,000 mt/a, only 7% did not attain the EPA faecal coliform standard but 31% of samples from large facilities (>45,000 mt/a) did not pass the standard. Three facilities had measurable E. coli-0157-H7 and were large site situated in commercial vegetable regions. One of these also possessed very high Clostridium perfringens, an obligate anaerobe indicative of wet, faecal conditions. We resampled and retested and it was still positive for E.coli-0157. PAH and phthalate content increased with increasing urbanization zones. Type of windrow vs. turning, size of handling and length of composting appear to be the significant controlling factors for hygiene quality with windrow and small facilities giving bes results.

Tab. 1: Characteristics of USA Green Waste Composts – Average (Min, Max)

SAMPLE REGION Salinity

dS m-1 % not passing EPA 503 Rule Quantity E. coli MPN g TS-1 E. coli 0157:H7 POS - NEG Cress Biomass % of Control Phthalate µg / kg PAH µg / kg Region I (WA) 6.2 (0.4 – 24 ) 23 2.1 * ( 0.2 – 7.4 ) not tested 46.7 ( 16 – 102) 103 (1 – 2,245) 156 (1 – 2,653 ) Region II (OR) 3.2 ( 0.2 – 11) 44 1.9 (0.4 – 6.6) POS (1) 93.3 ( 45 – 160 ) 2,275 (127 – 17625 566 ( 1 – 3,722) Region III (C ) 6.1 (1.2 – 17) 20 2.3 ( 1.9 – 7.3 ) POS (3) 55.4 ( 21 – 108) 5,373 (142 –20424) 1,628 (28 – 5,840)

* Bacteria are MPN and averages are geometric mean. If < MLD then sample is MLD ÷ 2.

Discussion & Conclusion

Of the 94 composts we tested, all varied enormously in test qualities, with 37% falling into a hygiene- restricted category by excessive pathogen indicators. Salinity and maturity appeared to be the greatest potential limit to improved horticultural use. Facility processing size and management are important factors for quality. More effort is needed to understand and regulate compost quality.

References

Blewett, C D. Roberts, W. Brinton (2005) Renewable Agric. Food Systems. 20, 67.

Brinton, W. (2004) in Proceedings of First World Congress Organic Food, Michigan State University, Mar 29-31 Doyle, M.P., M.C. Erickson (2006) in Microbe. ASM April

Heckman, J. (2006) Renew. Agric. and Food Systems 21, 143

Ingram,D.T., P.D. Millner. (2007) J.Food Protect. 70:4, 828

Yanko, W.A. (1988) Occurrence of Pathogens in Distribution and Marketing Municipal Sludges, EPA/600/S1- 87/014

Earthworms and Microorganisms: Disentangling the Black Box of