October 2013, Vol. 25, No.10

Gritty information 

Using data for more-effective preliminary wastewater treatment 

feature 1 art Joe Uglevich and Jimmie Griffiths
As any wastewater treatment professional will attest, grit can wreak havoc at a treatment facility. Yet rarely is the nature of grit quantified or understood before upgrade projects or new system designs are undertaken. Most process upgrades require extensive site-specific wastewater data (such as total suspended solids and biochemical oxygen demand), but the first step in the treatment train often is designed without taking these into account. Yet poor grit removal, handling, and processing equipment selection and performance can have significant effects on downstream unit processes. Read full article (login required) 


Bright lights, big city… smaller treatment systems? 

Determining the cost and energy incentives of decentralized treatment

feature 3 art Kartiki S. Naik and Michael K. Stenstrom

 With the increasing need for water reclamation, it is necessary to have a simple system, not only to reclaim wastewater but also to convey it to the respective area for reuse. Since reclaimed pipelines generally flow in the opposite direction of sewers, they usually have to gain some elevation in their course. Reducing the pipeline length is the principal solution used to minimize pumping-energy consumption. 

Centralized water resource recovery facilities (WRRFs) generally cannot be located close to all the potential reclaimed waste uses. It is especially difficult to establish such a large WRRF in any residential neighborhood. Thus, for centralized WRRFs, returning recycled water can require tremendous energy due to pumping. Adapting the design of a large facility to local reclamation needs to reduce pumping cost can be difficult. 

But what if one could optimize sewer networks and decentralized WRRF locations in an urban area to minimize pump-back energy consumption for recycled water? One research team computed pump-back energy consumption as a fraction of treatment and aeration energy for a hypothetical but realistic example in the vicinity of Hollywood, Calif. The team optimized the decentralized wastewater collection and treatment configuration for Hollywood for minimum energy consumption and cost. Read full article (login required) 


What is the right biomarker for water quality monitoring? 

Pros and cons of fecal coliforms, E. coli, and alternative microorganisms and how they are used in watershed monitoring and water quality improvements 

feature 4 art Ting Lu, Biju George, MaryLynn Lodor, Deborah Metz, James Parrott, James Fitzpatrick, Gary Hunter, Vikram Kapoor, and David Wendell

In the late 19th century, researchers developed the total plate count method for coliform colony counting as an indicator for pathogen and human health risk. By the mid-20th century, technologies were developed to distinguish total coliform, fecal coliform, and Escherichia coli. In 1986, the U.S. Environmental Protection Agency (EPA) recommended that E. coli be used as the indicator organism for recreational waters. In 2012, EPA recommended that both E. coli and enterococci be used for fresh waters. 

In the last few decades, advances in molecular tools have made it possible to identify and quantify a large number of bacterial species without having to culture them. 

A recent study undertaken by the Metropolitan Sewer District of Greater Cincinnati and the University of Cincinnati used biological water quality data — including fecal coliforms and E. coli along with some emerging pathogen indicators (Bacteroides, E. coli O157: H7, Norovirus, and Streptococcus) — to understand and identify pollution in the Duck Creek watershed with molecular tools (Kapoor et al., 2013). Read full article (login required) 


What’s the best fit?

Technical, environmental, and economic assessment of sludge-thickening processes 

feature 5 art Joshua J. Gable, Hiroko Yoshida, and Jae K. Park

Waste activated sludge (WAS) is characterized by low solids content, ranging from 0.25% to 2%, depending on operational condition. Prior to further stabilization processes, WAS often is thickened to increase total solids concentration to reduce the volume prior to anaerobic digestion, thereby decreasing the amount of energy required to mix and heat the solids. Several technologies are available for thickening WAS, such as gravity belt thickeners (GBTs), rotary-drum thickeners, dissolved-air flotation, and decanter centrifuges. 

Researchers wanted to compare conventional and novel thickening technologies in economic and environmental terms, carrying out the study in three steps. Read full article (login required) 


Operations Forum Features

Shaking the sand out 

Grit-removal design requires several considerations in facility retrofits and additions 

feature 2 art Robert J. Kulchawik

Grit-removal systems often are part of the first generation of unit processes at water resource recovery facilities (WRRFs). Some of these facilities are still in use, but many have gone through upgrades and are approaching 20 to 25 years in age. Because of the abrasiveness of grit, the operations and maintenance costs for these systems can be high. 

However, due to more-stringent effluent permit limits, many WRRFs are considering other advanced treatment processes, such as biological nutrient removal, membrane bioreactors, or other upgrades that can be adversely affected by the carryover and accumulation of grit.   

Thus, there is a greater need for grit systems to achieve higher removal efficiencies, either through retrofits or outright replacement. Retrofits and additions often can face several challenges, including limited space for construction of new processes, difficulty in maintaining existing grit removal during construction, phasing of tie-ins, and hydraulic limitations. Read full article (login required) 


Milford fights odor and corrosion 

Use of pure oxygen improves sewer system safety and operation 

feature 6 art Kenneth A. Bradstreet, Charles N. Smith, Robert P.G. Bowker, and Inken N. Mello

Milford, Conn., has an extensive sewer system that includes two water resource recovery facilities, 42 pumping stations, and an extensive system of sanitary sewers. In recent years, the system has been plagued with odor complaints and has undergone severe corrosion problems caused by hydrogen sulfide. 

Using a combination of pump station modifications and the addition of a pure-oxygen injection system the city has eliminated hydrogen sulfide production and thus odor and corrosion problems. Read full article (login required)