Water Environment Laboratory Solutions
upgrading from biological nutrient removal to enhanced nutrient removal (ENR). However, plant staff are concerned about whether such biological processes can be controlled tightly enough to produce an effluent that consistently contains only 3.0 to 4.0 mg/L of total nitrogen and 0.18 to 0.2 mg/L of total phosphorus.
Success will depend on accurate, real-time data for critical ENR parameters, such as dissolved oxygen, phosphorus, nitrate, nitrite, and ammonia. Automated process-control systems could help if operators were confident that the on-line probes used in such systems were accurate and reliable. Several on-line probes are available for these applications, but their accuracy, reliability, and maintenance requirements can vary.
So, as part of a pilot-plant study of a moving-bed bioreactor at the Blue Plains Advanced Wastewater Treatment Plant (Washington, D.C.), the project team spent 6 months evaluating how well three leading on-line probes monitored various process parameters.
Assessing the Bioavailability of Effluent Organic Nitrogen Using a Suite of Water-Quality-Based Assays
Eutrophication is an especially pressing problem in Chesapeake Bay where, despite years of effort, the restoration process has not met its goals. Continued water quality problems led to the signing of the Chesapeake Bay 2000 agreement, which mandated a 48% reduction (from 1985 levels) in nitrogen loads from point sources to the bay and its tributaries. This agreement has resulted in increasingly stringent effluent discharge limits for wastewater utilities discharging into the Chesapeake Bay watershed, down to as low as 3 mg/L total nitrogen (TN) by Jan. 1, 2011.
Facing enormous capital and operational costs to meet this discharge limit, the regulated community is interested in finding a way to determine and discount from TN loads the fraction of TN in effluent that is “recalcitrant.” Based on in-plant microbial processes, an argument has been made that effluent organic nitrogen (EON) is likely to be nonbiodegradable or “biologically unavailable” in the environment. Indeed, in Virginia, dischargers just recently can argue for an increased discharge cap if they can demonstrate that nitrogen in their effluent is not bioavailable. To safely apply this regulatory tool, it is necessary first to identify appropriate methods to assess the bioavailability of EON, not just to treatment plant microbes but also within a watershed, such as Chesapeake Bay, with a diverse microbial community.
Minor Changes; Major Improvements
A phased process controlled via changes in pH and oxidation–reduction potential vastly improves nutrient removal
When Bozeman, Mont., received its new Montana Pollutant Discharge Elimination System permit in 2008, the city found it had a new total nitrogen limit. Wastewater treatment plant effluent now had to contain less than 355 kg/d (782 lb/d) of total nitrogen, while the effluent ammonia limit was still 1.52 mg/L (30-day average) and 3.15 mg/L (daily maximum). So, plant staff had to figure out how to get the existing activated sludge system to cut effluent total nitrogen without sacrificing ammonia removal.
NEWS
U.S. EPA Releases ‘Nine POTW Study’ on Microconstituents
Last August, the U.S. Environmental Protection Agency (EPA) released the results of a small study that examined the occurrence of microconstituents in the influent and effluent of wastewater treatment plants. The project also included creating two new methods and revising and testing two existing ones.
This study, Occurrence of Contaminants of Emerging Concern in Wastewater From Nine Publicly Owned Treatment Works (EPA-821-R-09-009), commonly called the “Nine POTW Study,” sought to understand the extent to which certain chemicals, referred to collectively as “microconstituents” or “compounds of emerging concern,” may be entering water through publicly owned treatment works.
The Methodology Behind Standard Methods
The mysteries of differentiating between water analysis methods or determining the correct way to reference a method, in addition to the work behind the Standard Methods publication, have been revealed by American Water Works Association (AWWA; Denver) Standard Methods manager Steve Posavec.
Standard Methods for the Examination of Water and Wastewater was first published in 1905. The Standard Methods Committee, a group of more than 500 water and wastewater professionals, was charged with the review and approval of methods published in the book. The publication is the result of a joint effort by the American Public Health Association (APHA; Washington, D.C.), AWWA, and the Water Environment Federation (WEF; Alexandria, Va.).
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