Data from the state of New York reveal the factors that have increased or mitigated on-grid energy consumption at wastewater treatment plants (WWTPs) over the past 10 years, including the one mandate pushing demand higher.
With all the focus on energy efficiency, would it surprise you to find that aggregate energy use at WWTPs, at least in New York, is actually increasing? A study performed by the New York State Energy Research and Development Authority (NYSERDA) reveals the underlying energy drivers, which were jointly presented at WEFTEC 2015 by representatives from NYSERDA, Brown and Caldwell, and the Water Environment Research Foundation (WERF).
Though overall energy use will vary from state to state, the study indicates where a typical WWTP — based on size and activity, regardless of location — wins or loses on energy use. The research team arrived at their conclusions based on two NYSERDA energy assessments, a baseline report from 2003/04 and a follow-up report covering energy use through 2013. They found five factors in that 10-year span that shifted plant performance one way or the other. Through the pushing and pulling of energy saving and spending, the end result was a 3.7 percent increase in combined total annual electrical use at New York WWTPs.
First, the two big burdens on energy:
Nutrient removal – While nutrient removal isn’t practiced nationwide, mandates limiting phosphorus and nitrogen discharges have increased dramatically in the past 10 years, and will likely continue to proliferate across the country. Adding nutrient removal to WWTPs, typically at larger (75+ MGD) facilities, is a major reason why net energy usage increased in New York.
Plants operating below capacity – Due to consumers’ water conservation, water-saving plumbing fixtures, and infiltration and inflow (I&I), WWTPs in New York saw a decline in flow from 2003 to 2013. In fact, the majority of plants (100 out of 189) above 1 MGD experienced double-digit declines in the last decade. When plants operate below capacity and have fixed electrical base loads, energy use (and inefficiency) swells.
Fortunately, the effects of the above are mitigated by concerted efforts at many WWTPs to reduce energy usage.
The study credits the following three factors for having the most positive impact:
Level of interest – Ten years ago, there was much less talk about energy efficiency than there is today. The growing interest lies in its many benefits; most plant managers can find a good reason to become energy-efficient, whether for the operations budget, the environment, protecting scarce water resources, etc. Sheer will, guided by the understanding of these benefits, is the first step to reducing energy use, and NYSERDA’s survey found that more than half of respondents were “interested and engaged” in doing so.
Organizational energy initiatives – While small-scale energy improvements help, it’s the whole-plant approach, especially at large WWTPs, that really moves the needle on aggregate energy use. Plants striving for net-zero energy use are prime examples, but such ambition requires organizational change, or a ‘culture’ created around energy efficiency. The WEFTEC presenters noted that The Energy Roadmap, published by the Water Environment Federation (WEF), provides a ‘how-to’ for achieving organizational change.
Onsite generation – Perhaps the most obvious way to reduce strain on the electrical grid is to create your own energy through onsite generation, though the NYSERDA survey stated this trend to be slow-growing over the past decade. WWTPs are well-equipped, at least, with a number of ways to turn biosolids (sludge) into energy. There are certainly capital costs to get this done, however, and the downward trend on energy prices from the grid may serve to delay investment — or call it a disservice, depending on point of view.
The times they are a-changing, but the metrics in New York State suggest that the energy-efficiency movement may not be moving fast enough to offset new WWTP requirements and old inefficiencies.
Although necessary and ultimately inevitable, no one said culture change would be quick or easy.