A practical alternative to solidification with bulk amendments

The management of liquid waste material has always been a challenge, increasingly now with significant environmental over-site in all jurisdictions. Project managers working on infrastructure projects of all sizes including, underground utility renewal and replacement, transportation expansion, water security and safe energy transportation are required to establish plans for liquid waste management and disposal under a climate impact lens.

Liquid wastes generated from directional drilling, microtunneling and tunneling projects, hydro excavation, stormwater sediment extraction and environmental remediation fall into this category of problematic waste streams with a significant logistics component.

Historically, liquid waste materials have been dried up by adding vast quantities of dry amendments like sawdust, fly ash or lime to “soak up” or adsorb free liquids to create a dry material for handling and transportation.

Each of these materials may have a specific purpose but have been perpetuated because they are abundant and cheap. However, with the cost of transportation, tighter regulatory controls on disposal sites and waste characterization with beneficial re-use and diversion initiatives in place, bulking with dry amendments has become largely redundant.

Sawdust: an abundant, dry amendment waste material that is generated through timber milling operations. When sawdust is used as an adsorbent material, it creates a number of inefficiencies. Sawdust will have moisture variability due to different types of wood selected and climatic or environmental conditions inhibiting its adsorption capacity. As a result, vast amounts of sawdust are used in order solidify liquid waste material sufficiently for transportation. As an adsorbent, water will be released under pressure or in transportation. Finally, wood contains lignans and fatty acids and in excess amounts, can leach into aquatic ecosystems causing toxicity to the surrounding fauna.

Fly ash: a waste product resulting from the burning of coal is typically applied to, already contaminated wet material for landfill disposal. Fly ash can pose significant risk to human and animal health. It has a low pH and can contain toxic particulate. When fly ash is used to solidify liquid wastes, it will adsorb the liquid on the surface and will not encapsulate it. This means that over time the liquid will desorb from the fly ash and return to its original liquid state.

Quick lime: or calcium oxide, is a chemical reagent that has many purposes including acid neutralization, sulfur dioxide absorption and sludge stabilization. However, quick lime is highly corrosive and can pose a risk to the operators and equipment used in sludge stabilization. When quick lime comes into contact with water, it creates an exothermic reaction where heat is released and can reach temperatures as high as 70 °C. When quick lime is used as a solidifying reagent, a significant amount is required to be able to adsorb the liquid and may be unsuitable for variable liquid streams.

As an alternative to utilizing bulk amendments, superabsorbent polymers (SAP), engineered for speed and absorption optimization can have a significant impact in addressing waste minimization and opportunities for beneficial re-use. Non-toxic, environmentally friendly with dosage requirements between .25% and 2% by weight, the net total waste remains relatively the same as the original waste generated. Once the water is absorbed, it will not leach and the right SAP can be used effectively in variable waste streams with high or low suspended solids. Salt levels over 10,000 ppm and acidic or caustic environments will impact absorption rates but SAP is versatile in a broad range of waste characteristics.

 In conclusion, there are still waste streams where bulk addition is appropriate. However, with the current regulatory environment, transportation, disposal and the opportunity cost of not finding beneficial re-use opportunities for solidified liquid waste will continue to be problematic.

The utilization of the right SAP for the job can have significant cost saving implications on any project. Project managers, looking to simplify their waste management plans, will find SAP designed for their application a useful alternative.