In our previous blog, we defined ZLD, or Zero Liquid Discharge, as technologies which concentrate waste water until only solids and reusable “clean” water remains or, more broadly, which produce a “close to zero” amount of liquid waste.
As a sustainable solution this seems ideal, but as with with most technologies there are tradeoffs. When evaluating a technology such as ZLD, the evaluation must go beyond the perspective of a single company and also consider all the short- and long-term impacts on the environment. Environmental issues are often extremely complex, and the many various consequences of different solutions, such as ZLD technologies, must be considered in order to avoid creating new problems.
ZLD systems use a lot of energy. If their carbon footprint is too large, then the harm they do to the environment overall can outweigh the benefits of the treated waste water. ZLD systems are more viable in some situations than in others, and businesses and regulators need a consistent framework to help them decide whether or not ZLD technology is right for an individual business and the environment as a whole.
Each individual business needs to decide whether or not to implement a ZLD system by evaluating the internal costs involved. A ZLD system makes sense:
- where water is very scarce and/or where waste water is highly regulated,
- when an energy source, such as waste heat, exists which permits cost-efficient thermal treatment,
- and/or if the wastewater contains recoverable resources.
In order to achieve sustainable water management, a business also needs to anticipate the external cost, specifically the negative effects on the environment, associated with the ZLD system.
The Production-Integrated Water/Waste Water Technology focus group, or Piwa, which is part of the German network of experts in chemical engineering and biotechnology, has recently established a comprehensive ZLD decision framework which takes internal and external cost categories into account:
The decision framework (figure 1) takes into consideration not only business and economic criteria (marked in yellow) but also environmental criteria (marked in green) in order to determine whether a ZLD technology should be employed or not.
Legislators and regulatory authorities could also benefit from this sort of comprehensive decision making framework when writing and enforcing regulations. Simply put, if regulations are pushing businesses towards results, such as zero liquid waste, which are not achievable with current technology in a sustainable way, they are doing more harm than good. Stricter regulations should nurture new technological developments, but need to consider short- and long-term impacts on the environment as well.
This decision making framework makes sure that the concerns and interests of single businesses, the environment, and regulatory authorities are all taken into account in the decision making process, which will lead to an optimized solution.