As a member of WEAO, I have…

As a member of WEAO, I have been made aware of the draft legislation concerning the treatment and dewatering of septage in Ontario. I work with a Canadian company that manufactures dewatering presses that have been in use for many years in septage dewatering applications locally and in other Canadian and U.S. jurisdictions. We would like to address our comments, considering three (3) main topics of concern: 1. dewaterability of septage, alkaline-stabilized in the liquid form 2. cost of transport and application of liquid septage vs dewatered septage cake 3. feasibility of dewatering trenches in medium to large-scale operations 1.) Dewaterability of septage, alkaline-stabilized in the liquid form The draft legislation seems to imply that only alkaline stabilization would be an acceptable method of stabilization, and this, only while the septage is in its liquid form. With this, there are two issues: Transportation of liquid and alternate stabilization methods. As fuel and overall transportation costs rise, alternate methods of land-application or disposal favor dewatering of biosolids prior to application. With much of the overall component of septage being liquid (97.5% prior to alkaline stabilization, on average), disposing of this material consists mainly of transporting water. As alkaline stabilization tends to produce slurries that are very aggressive to dewatering equipment (of all types), future options with regards to the treatment methods of septage may be affected unless there is provision to allow mixing the alkaline material with dewatered septage cake. Alkaline materials tend to adhere to the areas surrounding orifices in dewatering devices in a process referred to as “blinding”. This blinding gradually reduces the opening size of the orifice, affecting the pass-through of liquids, thus the dewatering capacity of the device. Post-dewatering alkaline stabilization has been effectively performed in many jurisdictions across North America for many years. The process typically consists of a dewatering device which would remove 95% or greater of the solids fraction of the septage and a mixing device which would blend the dewatered “cake” and alkaline materials, which could be added in either a solid (powder) or liquid slurry form. Similarly, alternate stabilization methods, such as composting, have been carried out successfully for many years in many jurisdictions. It would be unfortunate if the MOE were to adopt legislation that would negatively impact future treatment alternatives by inferring that only liquid-state alkaline stabilization is acceptable. 2.) Cost of transport and application of liquid septage vs dewatered septage cake As inferred above, the cost of transportation is expected to remain high and even climb as fossil fuels remain in high demand. With each liter of liquid weighing approximately one (1) kilogram, on average only 25 grams of this total weight is contained in the solids fraction of conventional domestic septage. Thus, the cost of transport could be reduced dramatically if the solids fraction were separated from the liquid fraction prior to transport. The draft legislation would infer that only treatment in liquid form would be acceptable, so the hauler would have no choice but to transport the liquid septage to a treatment facility for further processing. It has been a common practice in many jurisdictions across North America to dewater the raw septage, leaving a liquid fraction that has a greatly reduced strength that is more willingly accepted for processing at municipal wastewater treatment facilities. The remaining dewatered “cake” can then be transported to a treatment facility at a fraction of the cost, reducing the financial impact on citizens and municipal utilities. The arrangement for this approach would consist of a dewatering device which would remove 95% or greater of the solids fraction of the septage and a truck loading or storage device which would allow transport of the cake to the nearest alkaline stabilization facility. There would also be provision to either transport the liquid fraction by sewer to the local wastewater treatment facility or by truck, as conditions permit. Furthermore, spreading dewatered cake as a method of land application has been demonstrated to be more environmentally friendly than the spreading of liquid waste. Cake can be applied at surface or by injection. Technological advances in dewatered cake injection systems and falling costs may foster more acceptance of this new method of applying biosolids. Again, it would be unfortunate if the MOE were to adopt legislation that would negatively impact future treatment alternatives by inferring that only liquid-state alkaline stabilization is acceptable, limiting possible application methods. 3.) Feasibility of dewatering trenches in medium to large-scale operations The draft legislation tends to infer that the only type of dewatering technology that would be acceptable is the dewatering trench, consisting of an un-lined ditch, through which the water would separate from the liquid as a function of the permeability of the soil. The draft legislation does not address other types of dewatering technology which can more rapidly separate the solid and liquid fraction, resulting in a higher capacity system that would suit medium to large-scale operations consisting of more than a single, small tanker truck. The arrangement for this approach would consist of a dewatering device which would remove 95% or greater of the solids fraction of the septage and a truck loading or storage device which would allow transport of the cake to the disposal or treatment site. There would also be provision to either transport the liquid fraction by sewer to the local wastewater treatment facility or by truck, as conditions permit. Such an operation would permit smaller hauling contractors to bring the septage to centralized detawering centres, setting up a scenario which would reduce overall environmental impact suggested by many separate, open trench-based dewatering sites. Such trench-based sites would be affected by weather conditions that could dramatically alter the time required to obtain that solids levels acceptable at suitable disposal sites, such as landfills. Dewatering the raw septage before treatment or disposal would not only lessen the environmental impact, the lower cost of transporting dewatered “cake” would have a positive financial impact on the municipality or organization responsible for the disposal of the septage. It would be unfortunate if the MOE were to adopt legislation that would negatively impact future treatment alternatives by inferring that only dewatering trenches are an acceptable method of dewatering septage. Conclusion As a company, we have been involved in septage dewatering applications since 1993. The first few installations of this type have been in Quebec, with later acceptance in British Columbia, New Brunswick and most recently in the United States, with private installations in Indiana, West Virginia, Pennsylvania and Texas. The environmental impact offered by first dewatering the raw septage and then further processing the dewatered “cake” and liquid “pressate” is much less than may be assumed from the methods suggested in the draft legislation. We are aware this information comes at a late stage in your process, however we would be happy to share with you our knowledge and experiences, both anecdotal and measured at the various facilities that dewater septage in this manner. We hope these comments serve to open possibilities for the MOE to consider alternatives to the stabilization and dewatering methods proposed by this draft legislation.

[Original Comment ID: 115730]