Alternate: Better Processes and Best Practices: Rethinking Thickening and Dewatering

The call to meet industry standards and operate according to best practices is one which all industry professionals can appreciate, but where standards are clearly outlined best practices is far less concrete. Within the residuals and biosolids treatment industry, that which constitutes best practices can vary greatly across facilities depending on a number of factors. In the spirit of diminishing this ambiguity, three case studies examining industrial dewatering and thickening systems at separate facilities will be presented. Two of the featured case studies will focus on dewatering; the first facility produces primarily inorganic residuals while the second facility's dewatering process treats starch-laden residuals. The third study also focuses on organic residuals and biosolids treatment, however their overall treatment involves a thickening process for relatively unique biosolids disposal which could be mutually beneficial for manufacturers and municipal processors alike. This presentation will include analysis of the technical aspects in each case study and a discussion of related findings. STUDY 1 DEWATERING INORGANIC RESIDUALS The subject of the first study is a facility which manufactures paint and coatings for electronic devices. In many treatment systems, flocculation is a vital step in dewatering solids. While this facility integrates flocculants, the waste stream composition poses additional challenges. Treatment begins in reactor tanks with coagulants, flocculants, and precipitants before being transferred to a clarifier. However, because this facility's residuals are predominantly inorganic, these residuals cannot effectively form the floc structure which renders a more manageable sludge suitable for common technologies like the belt filter presses or screw presses. Because popular technologies are ill-equipped to process this facility's distinctly tacky sludge, operators rely on a plate and frame filter press for dewatering (see Figure 1). Plate and frame filter presses are comparatively inexpensive, but despite cost-efficiency this press is subject to drawbacks which would typically disqualify its utilization in other facilities. These drawbacks, including reduced processing capacity and specific labor demands, are non-issues for this facility as operation occurs at a smaller scale. Because this sludge has a challenging consistency, the plate and frame filter press allows this plant to meet municipal limitations for proper disposal. Data obtained onsite reflected 2.0% feed solids was easily able to be dewatered to 28% cake solids, with a capture rate of 96%. STUDY 2 DEWATERING ORGANIC RESIDUALS The second study highlights a food processing facility which prepares potato chips. This facility's waste stream is marked by its high concentration of starch and starchy residuals. Due to the starch and water binding at an infinitesimal level, pressing alone cannot sufficiently dewater residuals. Therefore, this facility has incorporated a technology that may not adhere to wider perceptions of best practices. After its initial biological treatment in aeration basins, the waste solids are directed to a volute press. Onsite sampling reflected 2.1% feed solids was able to be dewatered to 17% cake solids but with a capture rate of only 79%. Figure 2 shows the cake from the volute press of this process. While volute presses may not meet high capture rates (see Figure 3), the resulting sludge does meet minimum requirements for municipal disposal. This choice could be seen as a failure to meet industry standards or best practices; however, this case study offers a fair example of a facility achieving balance between efficient operation and regulatory compliance. STUDY 3 THICKENING ORGANIC RESIDUALS The final case study features a second food processing plant. This plant, which produces a variety of sauces and condiments, has a waste stream with a high concentration of fats, oils and greases (FOGs). Processing FOGs can create undue strain on equipment, leading to wear and potentially shortening its operational lifespan. In this case, a complex system of treatment and retreatment is employed to maximize separation. The waste stream processing begins with an oil and water separator. After undergoing a biological process to remove contaminants, the waste stream moves to two dissolved air flotation devices (DAFs) which take 0.98% feed solids and thickens it to a 9.10% thickened solids product. Skimmed floatate, a gel-textured product shown in Figure 4, is transferred to a hopper. But what occurs next makes this study particularly noteworthy. Rather than disposing the end-process gel, this facility stores it in a silo onsite. Daily, the material is transported offsite to a nearby farm where the gel is applied as crop fertilizer. This stands out as an instance beneficial reuse, which is rare for industrial biosolids. This practice results in lower disposal costs for the facility. This beneficial reuse simultaneously benefits the municipal processers because the receiving POTW need not process FOG-laden wastewater or fine the facility for exceeding allowable effluent pre-treatment parameters. At a time when manufacturers in all areas are finding new and creative ways to meet corporate and social demands for sustainability, this type of process is an exemplar. However, as the previous case studies demonstrated this may not be in other manufacturer's' operational capacity or best interests. CONCLUSION Ultimately, the combination of unique waste streams, facility production capacity and local disposal options function in concert to outline best practices on an individual basis. The value of efficient operations cannot be overstated, but to truly thrive facility operators must be able to achieve maximum efficiency while also complying with oft-changing regulations. Failure to achieve this balance risks company resources and a cooperative relationship with municipal waste processors. By examining and comparing facilities' pre-existing treatment systems to post-upgrade systems against prevalent norms in the wider treatment landscape, we gain greater insight regarding the fluidity of best industry practices. This comparison will also yield a greater technical understanding for industry professionals as we compare capture rates and efficacy of various techniques across diverse waste streams' compositions. Finally, in addition to generating insights through analysis, this presentation will highlight how residuals and biosolids treatment systems impact municipal treatment facilities and vice versa. This discussion is intended to help reposition municipalities as a cooperative partner with a vested interest in the treatment process and industry.