Minimizing the Impact of Industrial Wastewater on the Environment and Your Budget
A Broader Concept of Sustainability May Help to Make the Right Call
The textbook definition of sustainability is ''avoidance of the depletion of natural resources in order to maintain an ecological balance." Embarking on the journey to achieve such a balance entails learning to look beyond the current predominant ''take, make, dispose" extractive model and turn it into a circular one. This new approach requires the industry to approach their manufacturing processes holistically; not only considering the balance of their own internal elements (basically water/energy/solids), but also looking at the broader impact that their activities have upon the environment. Aquatech has applied this approach to one of our upcoming projects in the United Kingdom, where our less intuitive scheme ended up being both the cheapest and most sustainable option. The result of this analysis prompted us to rethink the concept of sustainability in its broader sense, and is detailed below.
In this case, a consumers good manufacturer generates a highly volume wastewater stream. Since it doesn't have any onsite treatment, it currently disposes the as-is volume by truck. The impact of the wastewater on the factory's operations is mainly the associated disposal cost, but there is much more to consider from an environmental perspective. Specifically, the toll is quite high in terms of energy, chemicals (essentially energy) and the amount of solid waste sent to landfill. Additionally, the water discharged back to the environment is of lower quality than that originally supplied to the factory.
As part of their global sustainability strategy, the facility was eager to implement a solution which could help them reduce their disposal costs as well as their environmental impact. The most conventional approach for this kind of challenge is usually a local WWTP based on both chemical and biological treatment processes. Although this approach removes the energy required to transport the waste, the environment would still take a sizable toll.
Looking at the balance of the two scenarios above from an environmental perspective, we can say that
• The wastewater contains a lot of organic pollutants whose treatment call for a significant amount of energy
(mainly in form of chemicals for pretreatment and air for biological reactions)
• The transportation of the wastewater is not necessary to the treatment (yet with an important weight on the
balance) should be removed or limited.
Consequently, it seems that the best solution should both remove organics and limit the sludge volume to be dispose. The conventional scheme would not address either issue.
These thoughts led to an unexpected idea of integrating evaporation into our scheme. On one hand, an evaporator would require extensive energy and not treat organics. On the other hand, though, the process would concentrate the waste and subsequently reduce the hauling volume. In addition to this advantage, the concentrated waste could be treated by an anaerobic digester, which would address organics removal and produce methane biogas capable of partially offsetting the high energy costs of both processes. A detailed energy balance is included below.
The figures show that an energy-input intensive solution is the best solution for the environment, resulting in (a) net energy balance close to zero, (b) negligible use of chemicals (antifoam and pH adjustment only) and (c) no production of solid waste to landfill. On top of these benefits, the evaporator generates a fairly clean distillate suitable for reuse, further mitigating the ''depletion of natural resource." Last but not least, what about the factory's perspective? How could this high-energy technology be a good fit for them? Although the power needed to run the evaporator would be significantly higher than a conventional treatment based on process dynamics, there are quantifiable benefits with this arrangement. Three major ones include:
• Limited use of chemicals makes the system cheaper to run and safer for the operators.
• A single step treatment resulting in less operation and maintenance costs.
• No solid waste to worry about, further reducing the typical troubles of dewatering and associated costs.
When the facility stakeholders made their final decision, these factors prevailed. While the anaerobic digester was omitted from the final order, our client chose the evaporator due to the hauling cost savings and environmental benefits it would achieve. In conclusion, we found that evaporators will be most suitable in such applications where hauling cost is high, while the anaerobic treatment add-on will make sense when organic contaminant surcharges are also high. Opportunities like these have given us valuable experience for future low net-energy water reuse solutions in increasingly resource-conscious facilities.
