By Sally Brown, University of Washington
Abstracts of these resources are available in the searchable Information Portal offered to Northwest Biosolids members.
Comparing water quality trading programs: What lessons are there to learn?
Hydroeconomic modeling of resource recovery from wastewater: Implications for water quality and quantity management
Assessing cost-effective nutrient removal solutions in the urban water system
Discharge or reuse? Comparative sustainability assessment of anaerobic and aerobic membrane bioreactors
Achieving resilience through water recycling in peri-urban agriculture
It’s August and it’s hot. And depending where you live, pools are closed and beaches may even be closed. It may also be that you are somewhere where getting to a beach means getting on a plane. I am very fortunate because I have access to lovely refreshing lakes. For those that don’t I thought a library about water issues would be the closest that I could come to offering some summer relief. Last month was micro plastics. This month we focus on macro issues- NPDES permit compliance. That can mean evaluation of different technologies. It can mean considering resource recovery potential. It can also mean making new friends.
Let’s start with the making friends. Social isolation is a real thing these days. Who would have thought that problems meeting your discharge limits could open up new doors? Well one option to meeting those limits is to barter for them. The first paper goes into detail on trading options as a means to reduce OVERALL discharges of various pollutants to water bodies. Trading credits worked in the US for SO2 emissions and it is a viable option for water borne contaminants. Treatment plants are point source emitters. A majority of nutrient reaching water bodies are from non-point sources including agriculture and urban lawns. The authors go over a range of trading options by evaluating different functional trading programs. They talk about options and what has worked well and what hasn’t. When you are trading credits from a point source to non point sources, it is nearly impossible to verify compliance from the non point source. Here ratios are often used to guarantee that compliance has been achieved. For example you buy 1 nitrogen credit for a point source at a value of 2 nitrogen credits from non point sources as a way to assure that at least a 1:1 exchange has occurred. There are also examples of how credits change hands and what are the best ways to facilitate that this system works. For NPDES we typically thing of BOD, N and P but the authors have an example of trading for temperature in OR. In exchange for exceeding temperatures for discharge, the treatment plant exchanged for various stream mitigation measures including plantings to encourage shade. I like this article.
I don’t like this next article. Here the focus is on decision making at treatment facilities for achieving reductions in discharge. It reads like it is written by consultants who want to wow you by being way to abstract. This may happen to you at your plant- be aware. If you are a consultant- don’t do this! Point is you can work a system two ways, or you have two options. You can pick an option that recovers the most resources or you can pick an option that is able to treat the most water. This even has lots of equations and proofs (in the supporting information). The figure below shows your basic trade off.
Basically they are suggesting that focusing on nutrient recovery or focusing on expanding capacity are not one and the same.
The third article is one big step up from the second. Here the authors get very specific and do a sophisticated model considering a range of options to reduce nutrient discharge. They base their work on treatment plants in Fort Collins, CO. They consider realistic treatment options to reduce N and P in effluent. Adding Fe to reduce P and adding C to reduce N. They also talk about diversion of greywater before it gets to the plant and effluent reuse. The figure that sums up the results isn’t as clear as a bar chart but if you squint really hard, you get the point that there are many options and their model considered them all.
These are the consultants that I’d hire! They conclude : This research provides the framework and demonstrates the value in using an urban water system approach to identify optimal nutrient removal strategies that can be easily applied to other urban areas.
In other words, no silver bullet here, but a complicated solution that works better if you consider the whole picture.
Let’s say you are not quite up to a big picture. The 4th article compares aerobic membrane bioreactors (MBR) to anaerobic MBRs. Both are expensive options. Both have the potential to be used upstream from the treatment plant. Anaerobic MBR gives you energy but also a much higher nutrient effluent. If you can use that for fertigation that could be a good deal. The authors use an LCA to evaluate a fully version of the costs of each system.
One thing that all of these papers make clear is that if you use the effluent rather than discharge it, the NPDES problems go away. The final paper talks about a full system approach to water including effluent reuse with Sydney Australia as the focus. They include stormwater systems and a range of other options to provide a more sustainable approach to water management. And let me tell you that the beaches outside of Sydney are spectacular. As a reward for reading and to help get you through the summer, let me show you...