Who Will Take the 'Cake'? An Evaluation of Two Emerging Dewatering Preconditioning Technologies

In general, solids handling represents a significant portion of wastewater resource recovery facility operation and capital costs (Appels et al., 2008; Lau et al., 2013; Murugesan et al., 2014). Compounding this with challenges to dewaterability caused by biological phosphorus removal and other impacts from liquid treatment processes (Higgins et al., 2014), relatively low-cost options for preconditioning to improve dewaterability are worth considering. This presentation will evaluate two emerging technologies that have been reported to improve dewaterability: Orège's SLG® and HydroFLOW® USA Hydropath Technology (HydroFLOW®). These two technologies were featured in the 'Solids Pretreatment Methods to Enhance Dewatering Performance' fact sheet published by the WEF Residuals and Biosolids Committee's Solids Separation Subcommittee in 2019, and this presentation will provide updated data on the performance of these two emerging technologies. The first technology, Orège SLG®, is a pretreatment process which rapidly injects compressed air into biosolids which breaks up the Extracellular Polymeric Substances (EPS) and frees up water that was bound by it prior to dewatering. The air entrainment also reduces the density of the biosolids. Gases are stripped out from solution in the de-aeration step of the system. Reasons to consider implementing the Orège SLG® system include the following: - Improvement to dewaterability in terms of the following (see attached Table): An increase of cake solids, a decrease of polymer consumption, and/or an increase of dewatering hydraulic capacity. - Achieving some of the same dewaterability improvement benefits of Thermal Hydrolysis but in a smaller, lower cost, simpler, and safer manner. - Cleaner filtrate, resulting in less loading back to the plant. - Relatively low capital cost. - Low energy requirement (15 horsepower air compressor). - Any variation of sludge or biosolids can be successfully treated, including variations on primary versus secondary sludge blend, inclusion of industrial or fats/oils/grease, sludge thickness, type of digestion, and type of dewatering technology. - Improvement to viscosity, which is beneficial for enabling thicker sludge to be pumped and mixed. Orège also offers a version of SLG® that applies to thickening and is currently performing research and development for a version of SLG® with higher pressure that can achieve cell lysis to be applied prior to dewatering to achieve the benefit of higher volatile solids destruction in addition to improved dewaterability. The second technology evaluated, HydroFLOW®, induces an electric signal into liquid biosolids. This technology's primary function is to mitigate struvite buildup; however, with the installation of this technology, utilities have also reported better dewaterability in terms of decreased polymer consumption and/or increased cake solids. Reasons to consider implementing HydroFLOW® include the following: - Decreasing polymer consumption up to 25 percent. Increasing cake solids by up to 3 percent solids. - Cost-effective struvite mitigation. - Non-intrusive installation with no process downtime. - Very low capital cost. - Extremely low energy requirement (0.011 kW). Each technology will be discussed in terms of the current theories behind how they work, existing installations, current performance results, and return on investments experienced. Advantages and disadvantages of both technologies will be presented, which are based on operator experience, including one installation which has experience with the use of both technologies simultaneously. Finally, recommendations will be provided for when it may make sense to consider one or both of these technologies.