Test Method for Determining the Potential for Decomposition in Organic Soils

Wardwell, RE; Charlie, Wayne A.; Doxtader, K.G.

doi:10.1520/stp37344s

Cited by 15 publications

(28 citation statements)

References 2 publications

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“…These materials also have some general similarities with peat materials, with critical reviews of various total and effective stress strength testing for peat materials presented by Long (2005), Long and Boylan (2012), Mesri and Ajlouni (2007), O 'Kelly and Zhang (2013) and O'Kelly (2015a), to name a few. Although useful insights may be gained from analogies with peats and other highly organic soils, a degree of caution is required since significant physical differences exist between these materials, including the generally higher organic and fibre contents of peat and its significantly slower rate of biodegradation on-site (O'Kelly and Pichan, 2014;Wardwell et al, 1983) compared with biosolids and sewage sludge.…”

Section: Geotechnical Research Volume 3 Issuementioning

confidence: 99%

Geotechnics of municipal sludges and residues for landfilling

O’Kelly

2016

Geotechnical Research

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This paper presents a comprehensive review of reported field and laboratory investigations and theoretical work concerning the geotechnical behaviour/properties of water treatment residue (WTR), biosolids and sewage sludge materials, which are by-products of municipal water and wastewater treatment processes. After describing the backgrounds to the generation of these materials and various disposal options (with a focus on landfilling), including associated geotechnical issues, their physical, geotechnical index, compaction, undrained strength and effective-stress strength properties are described, including the effects of oxidation, biodegradation and viscous gellike pore fluid for biosolids/sewage sludge material. Characteristic compressibility, consolidation and permeability behaviour/properties are also presented for these materials and linked with microstructure and the chemicals added during the treatment processes. The paper then focuses on various geotechnical issues pertinent to landfill (monofill) disposal of these materials, including undrained strength requirements, design strength, on-site and laboratory strength measurements and water content-strength correlations. Since such correlations are material specific, with the geotechnical properties of biosolids, sewage sludge and WTR materials varying between water/wastewater treatment plants, they cannot be applied more widely with confidence. Alternative approaches to predicting undrained strength are described, including a power-law strength relationship with water content, which can be applied more generally. , 2008a). The type and amount of chemicals added depends on the nature of the source water, but primarily on its turbidity and hardness. The coagulants cause the colloidal particles present to aggregate into flocs (with the polyelectrolyte also acting as a binding agent to increase their inherent shear strength) that are more readily separated out by settling processes, removing not only the impurities but also the chemical additives. NotationThe residue so formed is categorised as aluminium sulfate (alum) or iron WTR material depending on the coagulant salt, with the former being the most widely used coagulant in the water treatment industry. Lime-softening sludge, composed of typically 80-95 wt% calcite (Raghu and Hsieh, 1986), is the result of softening hard water before its distribution as drinking water.Biosolids and sewage sludge materials are highly organic residue by-products of municipal waste water treatment, with the organic fraction originating principally from human faeces (primary sludge) and bacterial biomass (secondary sludge) and the inorganic fraction derived from materials such as soil, sediment and inorganic residuals (Haynes et al., 2009). According to the US Environmental Protection Agency (EPA) (2015), sewage sludge refers to the solids separated out during the treatment processes, whereas biosolids refers to treated sewage sludge material that meets regulatory pollutant-and pathogen-control requirements for land applica...

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Section: Geotechnical Research Volume 3 Issuementioning

confidence: 99%

Geotechnics of municipal sludges and residues for landfilling

O’Kelly

2016

Geotechnical Research

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“…In situ peat has an extremely high water content, ranging from a few hundred per cent of dry mass to greater than 2000% (Hobbs, 1986), which results in characteristic low strength and high compressibility (O'Kelly, 2006a;Mesri and Ajlouni, 2007). Decomposition or biological oxidation in peat produces a permanent material change whereby large fibres and plant cellular structures are broken down, adsorption complexes on the cell walls are weakened (Wardwell et al, 1983), pore space decreases in size and the proportion of fine material increases (Blackford and Chambers, 1993), ultimately producing an amorphous granular material. However, the decomposition rate is generally extremely slow under normal subsurface conditions on account of the non-conducive environment of natural ecosystems.…”

Section: Introductionmentioning

confidence: 99%

Stimulated decomposition in peat for engineering applications

Pichan

O’Kelly

2013

Proceedings of the Institution of Civil Engineers - Ground Impr

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Peat deposits are highly compressible, undergoing significant long-term settlement, particularly for fibrous peat.Since decomposition of organic matter can have a significant effect on compression behaviour, the ability to artificially stimulate and pre-decompose a bearing peat stratum prior to the main construction works may mitigate against increased compression rates reported to occur over the design life. This paper presents a feasibility trial of a technique that accelerates the decomposition process in peat prior to entering into full laboratory and field testing.The main decomposition limiting factors of pH and carbon:nitrogen (C:N) ratio are adjusted by adding sufficient amounts of basic and nitrogenous materials. The proposed technique can be tailored for specific peat deposits and can also be achieved in a more sustainable manner. In the trial on moderately decomposed fibrous Sphagnum peat, different peat blends were prepared using additives of peat pulverised fuel ash (PPFA) and urea. Optimum C:N ratio and pH for decomposition were achieved by adding ,21 kg PPFA and ,1 . 5 kg urea per cubic metre of wet peat. The availability of natural decomposers in the peat was also confirmed pre-and post-treatment using a plate count technique, with measured microorganism populations of the order of 10 5 colony-forming units (CFU)/g dry peat.

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“…It has been well documented in the literature (e.g., Mesri and Ajlouni, 2007;O'Kelly and Pichan, 2013;Wardwell et al, 1983) that the decomposition process causes progressive degradation of constituent fibres and hence a reduction in fibre content. Overall, this trend is evident in Figure 7 for both the peat and blended material, particularly for aerobic incubation, with best-fit trend lines indicating a general trend of decreasing fibre content with increasing incubation period.…”

Section: Physical Properties Of Test Materials After Incubation Treatmentioning

confidence: 99%

“…carbon dioxide and water). The process is accompanied by permanent material changes, including progressive destruction of constituent fibres; disappearance of physical structure/fabric; reduction in water-holding capacity; weakening of adsorption complex; gas generation and reduction in volume of the solids (Mesri and Ajlouni, 2007;O'Kelly and Pichan, 2013;Wardwell et al, 1983). After larger particles have been broken down by earthworms/insects/snails etc.…”

Section: Introductionmentioning

confidence: 99%

“…Recent developments in microbiology have also indicated that biological activity can be promoted by injecting nutrients (e.g., glucose) or by changing environmental conditions (Mitchell and Santamarina, 2005). Preliminary laboratory trials on the feasibility of artificially induced decomposition in fibrous peat by O'Kelly (2012, 2013) have indicated that its main decomposition limiting factors of carbon-to-nitrogen (C/N) ratio and pH level can be adjusted within reported optimum ranges of 25-30:1 and 7•0-7•5, respectively (Wardwell et al, 1983), by mixing sufficient amounts of basic and nitrogenous materials with the peat.…”

Section: Introductionmentioning

confidence: 99%

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Effect of decomposition on physical properties of fibrous peat

O’Kelly¹,

Pichan²

2014

Environmental Geotechnics

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22Organic matter in peat deposits undergoes slow microbial decomposition, which causes permanent material change, including reduction in volume of solids, and is a significant factor in the development of creep settlements for such deposits. Microorganisms accountable for decomposition are readily available in peat, although generally less populous compared with other soils on account of the unfavourable environment. This paper presents a novel experimentallaboratory study that stimulates the growth of microorganisms in a fibrous peat and hence its decomposition rate.The carbon/nitrogen ratio and pH value of the peat were adjusted within optimum ranges for microbial activity to occur by blending sufficient amounts of pulverised fuel ash and urea with the wet peat. This process did not adversely affect indigenous microbial populations within the peat. Blended material was incubated aerobically and anaerobically at 30°C over periods of up to 126 days. Microbial populations increased by approximately 3500-and 1800-fold under aerobic and anaerobic incubation, respectively, which was an indicator of increased decomposition rate. Water content, specific gravity of solids, volatile organic content and fibre content were measured both before and after incubation treatment. Fibre content was found to be approximately inversely proportional to incubation period, with relatively greater reductions in fibre content occurring for blended material under aerobic conditions.

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Test Method for Determining the Potential for Decomposition in Organic Soils

Cited by 15 publications

References 2 publications

Geotechnics of municipal sludges and residues for landfilling

Geotechnics of municipal sludges and residues for landfilling

Stimulated decomposition in peat for engineering applications

Effect of decomposition on physical properties of fibrous peat

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