Effective microorganism

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An effective microorganism (EM) refers to any of the predominantly anaerobic organisms blended in commercial agricultural amendments or for environmental applications such as for septic tanks. EM technology is purported to support sustainable practices in farming, improve composting operations, septic tank performance, efficiency of wastewater treatment plants and to reduce environmental pollution.

Many of the "additives" used for improving the performance of sanitation systems, namely pit latrines, septic tanks and wastewater treatment plants, are also based on effective microorganisms. Despite the claims made by manufacturers, available studies which have used scientific methods to investigate these additives have come to the conclusion that long-term beneficial effects are not proven.

Possible constituents[edit]

One trademarked product was originally marketed as EM-1 Microbial Inoculant.[1] Such EM blends include:[2]


The concept of "friendly microorganisms" was developed by Professor Teruo Higa, from the University of the Ryukyus in Okinawa, Japan. He reported in the 1980s that a combination of approximately 80 different microorganisms is capable of positively influencing decomposing organic matter such that it reverts into a "life promoting" process. Higa invoked a "dominance principle" to explain the effects of his "Effective Microorganisms". He claimed that three groups of microorganisms exist: "positive microorganisms" (regeneration), "negative microorganisms" (decomposition, degeneration), "opportunist microorganisms". In every medium (soil, water, air, the human intestine), the ratio of "positive" and "negative" microorganisms is critical, since the opportunist microorganisms follow the trend to regeneration or degeneration. Therefore, Higa claimed that it is possible to positively influence the given media by supplementing with "positive" microorganisms.

Validation attempts[edit]

The concept has been challenged and no scientific studies support all of its claims. This was acknowledged by Higa in a 1994 paper co-authored by Higa and soil microbiologist James F Parr. They conclude "the main limitation...is the problem of reproducibility and lack of consistent results.".[3]

Parr and Higa mention soil pH, shading, soil temperature and flooding as factors affecting the interaction of EM with local microorganisms and with each other. The approach that Higa and Parr recommend is maintaining pH and soil temperature within conditions known to be detrimental to negative microorganisms as well as the addition of EM to tip the balance of positive and negative microorganisms in favor of the former.[citation needed]

They dismiss inoculants that include only a single microorganism as generally ineffective due to the uncertainty about the conditions in which a single microorganism would be effective.[3] They cite the acknowledgment by the scientific community that multiple microorganisms (as in the case of Bokashi, invented and marketed by Higa) in coordination with good soil management practices positively influence plant growth and yield.

Various researchers have examined the use of EM in making organic fertilizers and investigated the effects of the fermented organic fertilizer on soil fertility and crop growth. The resulting effects on crop growth depend upon the organic fraction, direct effects of the introduced microorganisms, and indirect effects of microbially-synthesized metabolites (e.g., phytohormones and growth regulators).[4][5][6][7][8][9]

The use of EM in the bokashi-intensive composting process for home kitchen waste has been in use in Christchurch, New Zealand for years, backed by the local city council.[citation needed]

Due to the fact that only very few studies exist which have used scientific methods to investigate additives based on EM, any claims made by manufacturers regarding long-term beneficial effects need to be treated with care.

Use in sanitation systems[edit]


Effective microorganisms are advocated for use in sanitation systems, in particular in pit latrines and septic tanks. The concept has similarities to that of "pit additives" or "septic tank additives" although EM proponents claim that EM includes a much wider range of constituents than most such additives. Most of these additives claim EM aspects, although some are simply used to improve odor or to reduce fat build-up. The products, consisting of packaged micro-organisms or enzymes or both, are marketed for their ability to either reduce the pit or septic tank filling rate with fecal sludge, or to decrease material volumes.

It has been estimated that in the U.S. more than 1,200 septic system additives were available on the market in 2011.[10] However, very little peer-reviewed and replicated field research exists regarding the efficacy of biological septic tank additives.[10]

Claimed benefits[edit]

The claims frequently made by manufacturers or sales personnel about these additives include:[11]

  • The products contain micro-organisms that can biologically break down the material in the pit to harmless compost products.
  • Nutrients present in the additive ensure optimal growth conditions for micro-organisms to break down pit contents.
  • Additives stimulate the micro-organisms in the pit accelerate sludge breakdown.
  • Aerobic micro-organisms create aerobic conditions in the pit that result in rapid degradation and reduced odor.
  • Non-pathogenic bacteria out-compete and/or eat pathogenic microorganisms.
  • Odours are reduced as a result of aerobic breakdown.

However, South African research during 2010-2012 as well as Netherlands research in 2013-2014 conclusively showed that it is very unlikely that such claims are valid.[11][12] The quantity of bacteria introduced to the pit or septic tank by dosing additives turned out to be insignificant compared to the number already present.[11]

Wastewater treatment plants and septic tanks[edit]

Proponents of EM claim that adding effective organisms to wastewater can facilitate reduction in organic load and pathogen removal, leading to significant improvements in effluent quality. They also claim benefits relating to the rate of sludge build-up and odor reduction. One source claims that EM can reduce hydrogen sulphide and ammonia production.[3] Their reasoning is that EM mixtures contain natural’ organisms that prevail over the rather less ‘natural’ organisms that would otherwise dominate conditions in the treatment unit, whether this be a septic tank or some form of aerobic treatment. They even claim that by overcoming the effects of ‘unnatural’ substances such as bleach and other disinfectants, addition of EM allows septic tanks and other treatment systems to function in conditions that would otherwise have resulted in their becoming ‘dead’ and non-functional.

One short note claims that EM microorganisms contain various organic acids due to the presence of lactic acid bacteria. These secrete organic acids, enzymes antioxidants, and metallic chelates thus create an antioxidant environment, which assists in the enhancement of solid-liquid separation, which is the foundation for cleaning water.[13] The authors of the note provide no explanation of how this works.

However, the findings from various studies around the world indicate that:

  • There is no reliable evidence that addition of EM solutions to wastewater prior to treatment has a significant effect on pathogen concentrations.
  • The evidence on the effect of EM solutions on settleability of solids and reduction in effluent BOD and SS is mixed. Under some circumstances, it appears that adding EM can have some effect on both BOD and SS concentrations but the effect is not large and is not proven.
  • The available evidence suggests that any lasting effect of EM is dependent on regular application of EM organisms combined with good maintenance of the treatment technology. This will require (a) a reliable supply chain for the EM material and (b) management systems that ensure that the EM material is added regularly and on schedule.

While it is possible that EM techniques can lead to some improvement in effluent quality, it is unlikely that the improvement obtained will be sufficient to allow effluent uses that would not have been possible if EM had not been added. In particular, it seems that any claim that EM use can make otherwise ‘unsafe’ effluents from primary and enhanced primary treatment process ‘safe’ is unlikely to be justified.


Australian scientists investigated the effect of the addition of EM to a wastewater treatment plant and a number of septic tanks.[2] Their aim was to test the hypothesis that EM reduces sludge volumes. They found significant reduction in pH levels at the wastewater treatment plant together with improved settlement of sludge but with a significant increase in organic matter (measured as biological oxygen demand). Their results for the septic tanks showed a homogenization of conditions in the tanks after EM application, which they suggested was due to domination by a particular type of micro-organism. However, they found no reduction in suspended solids concentration in the effluent and concluded that there were not sufficient changes in sludge volume in the wastewater treatment plant or suspended solids in the septic tanks to indicate a clear benefit from the use of EM in wastewater.

Orangi Pilot Project in Karachi, Pakistan[edit]

A project in Karachi, Pakistan called the Orangi Pilot Project (OPP) has beeing making use of EM technology. The OPP promotes a treatment technology comprising a two-chamber tank. The first of these acts like the first compartment of a septic tank while the second is filled with gravel to provide filtration. It is not clear whether flow through the second compartment is upward or downward. This arrangement has some similarities to baffled reactor designs promoted by the German NGO BORDA, although standard BORDA designs provide more chambers, arranged in series and with all after the first chamber operating in an upward flow mode. The baffled reactor design is one of a number of ‘DEWATS’ (decentralised wastewater treatment systems) wastewater treatment technologies promoted by BORDA. All operate anaerobically and are examples of what might be termed enhanced primary treatment. If maintained well, enhanced primary treatment modules should perform better than a well maintained conventional septic tank but will still produce an effluent with high pathogen levels and relatively high biological oxygen demand and suspended solids concentrations.

The OPP is using EM techniques to improve the effluent produced at these small treatment plants, including the plant that treats effluent from a nursery in Karachi. It has also supported the installation of several small treatment plants using EM technology in rural Sindh and Punjab. Its partner organization Ali Hasan Mangi Memorial Trust (AHMMT) installed a small EM sewage treatment unit to treat sewage from 300 houses in the village Khairodero in Larkana District. Another eleven are reported to be functioning and more are planned.[14]

During discussions at the Urban Resource Centre in Karachi in late 2011, the late Parveen Rehman of OPP stated that the addition of EM to the inlet chamber of these treatment facilities had resulted in improved effluent quality and a significant reduction in smell. However, it seems that OPP had not attempted to quantify the improvement and had not made any formal assessment of the effect of EM treatment on effluent quality.

US Environmental Protection Agency (EPA)[edit]

The US Environmental Protection Agency (EPA) has produced a fact sheet on the use of additives to improve the performance of septic tank treatment systems. This is concerned with biological additives in general rather than EM in particular.[15] The fact sheet concludes that biological additives such as bacteria and extracellular enzymes do not appear to significantly enhance normal biological decomposition processes in septic tanks. They go on to say that ‘some biological additives have been found to degrade or dissipate septic tank scum and sludge. However, whether this relatively minor benefit is derived without compromising long-term viability of the soil infiltration system has not been demonstrated conclusively’. They noted that some studies suggest that material degraded by additives in the tank contributes to increased loadings of BOD, suspended solids, and other contaminants in the otherwise clarified septic tank effluent.

North Carolina, USA[edit]

Researchers from the U.S. carried out field experiments in 2011 to assess the effect of additives on the performance of 20 septic tanks.[10] These septic tanks served residences at a mobile home park located in Orange County, North Carolina were used in this study. The researchers distinguished between tanks that were well maintained, poorly maintained and maintained to an intermediate level, defining the level of maintenance in terms of the period since the septic tank had last been desludged (up to 2–3 years for well maintained, 15 – 20 years for poorly maintained and somewhere in between for the intermediate category). They found some reduction in sludge accumulation rates but only for their category of well-maintained septic tanks. A follow up study investigated the impact of three additives on the performance of well-maintained septic tanks. Overall, their conclusion was that there was limited evidence of additive impact on the performance of septic tanks. It should be stressed that these field experiments used additives other than EM and the proponents of EM would no doubt argue that the more varied composition of EM makes it more effective than the additives tested here.

Cost aspects[edit]

Based on the research conducted so far, it is fair to say that individuals and local authorities spending money on such additives for their sanitation systems are generally wasting their money.[11] A fifth of South African municipalities indicated in 2011 that they purchased various additives as part of their sanitation management programmes. However, the Water Research Commission in South Africa advocates against this practice, stating that the money would be better spent on effective pit sludge management through improved pit emptying methods and improved pit design, or by use of movable top structures or low flush toilets with alternating leach pits.[16]

As the costs and health risks associated with manual pit emptying are significant, if a product was ever developed which significantly impacted the filling rate of pits, e.g. based on EM, this would be of enormous significance.[11]

Use to reduce environmental pollution[edit]

  • In India, effective microorganisms have been used in an attempt to clean up some sewage-polluted lakes in Bangalore in 2015.[17]
  • After the Bangkok floods of 2011 EM was used to clean up polluted water.[18]


  1. ^ "Trademark Guidelines". emrojapan.com. 2011. Retrieved 13 November 2011. 
  2. ^ a b Szymanski, N.; Patterson, R.A. (2003). "Effective Microorganisms (EM) and Wastewater Systems in Future Directions for On-site Systems: Best Management Practice." (PDF). In R.A. and Jones, M.J. (Eds). Proceedings of On-site '03 Conference. Armidale, NSW, Australia: Lanfax Laboratories. pp. 347–354. ISBN 0-9579438-1-4. Retrieved 2006-11-14. 
  3. ^ a b c Higa, Dr. Teruo; Dr. James Parr (1994). Beneficial and Effective Microorganisms for a Sustainable Agriculture and Environment. Atami, Japan: International Nature Farming Research Center. p. 7.  External link in |title= (help);
  4. ^ Yamada, K.; Xu, H. L. (2001). "Properties and Applications of an Organic Fertilizer Inoculated with Effective Microorganisms". Journal of Crop Production 3: 255. doi:10.1300/J144v03n01_21. 
  5. ^ Pei-Sheng, Y.; Hui-Lian, X. (2002). "Influence of EM Bokashi on Nodulation, Physiological Characters and Yield of Peanut in Nature Farming Fields". Journal of Sustainable Agriculture 19 (4): 105. doi:10.1300/J064v19n04_10. 
  6. ^ Xu, H. L. (2001). "Effects of a Microbial Inoculant and Organic Fertilizers on the Growth, Photosynthesis and Yield of Sweet Corn". Journal of Crop Production 3: 183. doi:10.1300/J144v03n01_16. 
  7. ^ Xu, H. L.; Wang, R.; Mridha, M. A. U. (2001). "Effects of Organic Fertilizers and a Microbial Inoculant on Leaf Photosynthesis and Fruit Yield and Quality of Tomato Plants". Journal of Crop Production 3: 173. doi:10.1300/J144v03n01_15. 
  8. ^ Daiss, N.; Lobo, M. G.; Socorro, A. R.; Brückner, U.; Heller, J.; Gonzalez, M. (2007). "The effect of three organic pre-harvest treatments on Swiss chard (Beta vulgaris L. Var. Cycla L.) quality". European Food Research and Technology 226 (3): 345. doi:10.1007/s00217-006-0543-2. 
  9. ^ Daiss, N; Lobo, M. G.; Gonzalez, M (2008). "Changes in postharvest quality of Swiss chard grown using 3 organic preharvest treatments". Journal of food science 73 (6): S314–20. doi:10.1111/j.1750-3841.2008.00842.x. PMID 19241576. 
  10. ^ a b c S. Pradhan, Michael T. Hoover, G.H. Clark, M. Gumpertz, C. Cobb, J. Strock (2011) Impacts of biological additives; Part 2 Septic Tank Effluent Quality and Overall Additive Efficacy, Journal of Environmental Health, Volume 74, Number 5, p. 22-28
  11. ^ a b c d e Foxon, K., Still, D. (2012). Do pit additives work? Water Research Commission (WRC), University of Kwazulu-Natal, Partners in Development (PiD), South Africa
  12. ^ Grolle, K. (2015) Laboratory investigations into solids solubilisation of black water and faecal matter: Effect of additives and internal physical chemical pit latrine aspects, Department of Environmental Technology and Research, University of Wageningen, Wageningen, The Netherlands
  13. ^ Higa, T. & Chinen, N. 1998, ‘EM Treatments of Odor, Waste Water, and Environmental Problems’, College of Agriculture, University of Ryukyus, Okinawa, Japan.
  14. ^ "Untitled Document". oppinstitutions.org. 
  15. ^ EPA 625/R-00/008 Onsite Wastewater Treatment Systems Special Issues Fact Sheet 1 - Septic Tank Additives
  16. ^ Still, D., O’Riordan, M. (2012). Tackling the challenges of full pit latrines - Volume 3: The development of pit emptying technologies. WRC Report No. 1745/1/12, ISBN 978-1-4312-0293-5, Water Research Commission, South Africa
  17. ^ Mohit M Rao. "Micro bugs may help in restoring our embattled water bodies". The Hindu. 
  18. ^ "EM balls produced by royal project". The Nation. 2 November 2011.