Engineering Behavior of Water Treatment Sludge

2005

Waste Management

The mechanical properties of dewatered, anaerobically digested sewage sludge were determined from soil laboratory tests. The sludge material is largely composed of organic clay sized-particles, a sizable fraction of which is in an active state of biological digestion which can continue over many years under field conditions. Moderately digested sludge material was found to have a typical specific gravity of solids value of 1.55, and loss on ignition (LOI) value of 70% dry mass. Strongly digested sludge, produced by digesting the liquid sludge further at 35 o C in the laboratory, was found to have a lower LOI value of 55% dry mass, and a higher specific gravity of solids value of about 1.72. The maximum dry density of 0.56 tonne/m 3 for the dried sludge material was produced using standard Proctor compaction at roughly 85% moisture content (54% solids content).Air-dried, compacted sludge material was tested in quick-undrained, triaxial compression and vane shear. Undrained shear strength-moisture content plots are presented. Shear strength values measured in triaxial compression and vane shear were consistent. The effective angle of shearing resistance (') was determined from consolidated-undrained, triaxial compression tests on pasteurized, normally consolidated samples of the sludge material. The mechanical properties of the sludge material changed with the level of sludge digestion. The ' value increased from 32 o for moderately digested sludge, to 37 o for strongly digested sludge. The effective cohesion of the sludge material remained zero throughout.The shrinkage, swelling and adhesion properties of the sludge material were also studied. Significant shrinkage occurred as the compacted material dried. The sludge material lost its adhesion below about 95% moisture content (51% solids content). Re-hydration of the dry material caused the bulk volume to double.

Section: Index Propertiessupporting

confidence: 86%

Mechanical properties of dewatered sewage sludge

2005

Waste Management

“…The very high liquid and plastic limit values and colloidal activity (the plasticity index to clay fraction ratio) were similar in some respects to those of highly humified peat (Skempton and Petley, 1970). Comparable liquid and plastic limit values have also been reported by Miura et al (1985) and Wang et al (1992) for water treatment sludge and by Charlie (1977) for paper mill sludge. Ignition of the dry powdered sludge material in a muffle furnace at a temperature of 440 o C produced a 70 % reduction in the mass of the test specimen.…”

Section: Index and Physical Propertiessupporting

confidence: 76%

Geotechnical properties of municipal sewage sludge

2006

Geotech Geol Eng

The geotechnical properties of municipal sewage sludge, in particular those pertinent to the handling and landfilling of the material, are presented. Index, drying, compaction, shear strength and consolidation tests were conducted on the material at different states of biodegradation. The organic content and specific gravity of solids were found to be inversely related, with typical organic contents of 50-70% and specific gravity of solids of 1.55-1.80. The density of the compacted material was low in comparison with mineral soils. Standard Proctor compaction yielded a maximum dry density of 0.56 tonne/m 3 at 85% water content. Laboratory vane-shear and triaxial compression tests indicated that, below about 180 % water content, the shear strength of the sludge material increased exponentially with reducing water content. Consolidated-undrained triaxial compression tests on the pasteurised sludge material indicated an effective angle of shearing resistance of 32 o for the moderately degraded material and 37 o for the strongly degraded material. Biogas was produced at rates of up to 0.33-litres/day/kg slurry due to ongoing biodegradation and the pore water pressure response must be taken into account in any stress analysis. Consolidation tests using the hydraulic consolidation cell, oedometer and triaxial apparatus indicated that the sludge material was highly compressible although practically impermeable, for example the coefficient of permeability for the moderately degraded slurry was of the order of 10 -9 m/s. However, creep deformation was significant with typical coefficient of secondary compression values of 0.02-0.08 for the compacted material. A more free-draining material was produced at higher states of biodegradation.

“…Further, they typically exhibit very low shear strength, very high compressibility, swelling and shrinkage potentials and have very to extremely low permeability (Arulrajah et al (2011, Aydilek et al (2000), Chen et al (2014), Diliūnas et al (2010), Disfani et al (2013Disfani et al ( , 2015, Kayser et al (2011), Klein and Sarsby (2000), Koenig and Bari (2001), Lin et al (2014), Lo et al (2002), O'Kelly (2006O'Kelly ( , 2008aO'Kelly ( , 2008bO'Kelly ( , 2010O'Kelly ( , 2013aO'Kelly ( , 2014aO'Kelly ( , 2016aO'Kelly ( , 2016b, Quille (2009, 2010), Wang et al (1992), Wang and Tseng (1993), Wichmann and Riehl (1997), Zhan et al (2014), to name a few). For landfilled material, chemicals added during the water/ wastewater treatment processes tend to enhance the strength properties but reduce the level and rate of consolidation achievable on-site (O'Kelly and Quille, 2010).…”

Section: Typical Geotechnical Behaviourmentioning

confidence: 99%

“…Management of these increasing amounts of sludge and residue materials is a key issue. Principal disposal options for these materials are ■ indefinite storage in shallow or deep lagoons (Claydon et al, 1997;Klein and Sarsby, 2000;Lin et al 2014;Zhan et al, 2014) ■ volume reduction by mechanical and (/or) thermal means followed by landfilling, either at dedicated monofills (O'Kelly, 2004(O'Kelly, , 2005b(O'Kelly, , 2010(O'Kelly, , 2016dLin et al 2014;Wang et al, 1992;Zhan et al, 2014), dedicated deposition areas at sanitary landfills (O'Kelly, 2008a) or co-disposal with municipal solid waste (MSW) in which these residue materials are usually intermixed with MSW streams (Koenig and Kay, 1995;Koenig et al, 1996;Lo et al, 2002;Loll, 1986Loll, , 1991) ■ the preferred route of beneficial use as agricultural land fertiliser (Elliott et al, 1990), for composting to produce a humus-like product resembling soil, in forestry and soil redevelopment (e.g. mine reclamation) ■ incineration.…”

Section: Management Of These Waste Streams and Principal Disposal Optmentioning

confidence: 99%

“…However, in practice, the 300% maximum water content requirement is generally not a reliable guide for achieving minimum shear strengths necessary for landfilling. For instance, O'Kelly and Quille (2010) reviewed undrained strength against water content data presented for different alum WTR materials by Novak and Calkins (1975), Wang et al (1992), Wichmann and Riehl (1997) and O'Kelly (2008a). They found that the undrained strength of these materials ranged 6-80 kPa at 300% water content.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Geotechnics of municipal sludges and residues for landfilling

2016

Geotechnical Research

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...