The WEF Sustainable Utilities Task Force presents a resource for utility managers seeking examples of succesful sustainability practices

Energy Efficient MBR Designs Can Significantly Reduce Operating Costs


The MBR technology is an attractive, flexible solution for plant expansion/enhancement
as well as for greenfield facilities. While capital costs of MBRs have become fairly
competitive with conventional treatment systems, the operating costs, specifically energy
requirements, require additional focus. In order to provide the most cost effective and
energy efficient system, enhancements with design, operations, and equipment selection
are required. There are several areas within the design of an MBR plant which provide the
opportunity for a cost effective design which balances capital and operating costs. These
include use of primary clarification, use of flow equalization, adjusting the balance of the
solids between biological treatment and the membrane basins, and pump configuration.
Key operational focus areas include membrane scour air operational strategies, use of flux
enhancers, optimization of the number membranes in service, and biological operating
conditions. Along with the operational strategies to reduce energy, energy efficient
equipment must be selected.


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Posted: May 20th, 2011 | Filed under: Stormwater, Waste Water Treatment, Water Treatment | Tags: , , , , , | No Comments »

Optimization of Air Flow in a Deep Tunnel System for the City of Los Angeles

City of Los Angeles
Los Angeles, California

This paper discusses the development of a unique sewer tunnel ventilation strategy for a future
City of Los Angeles wastewater project in the northern part of the City’s service area.
Air accumulation in sewer tunnels can be a major issue due to high air volumes generated both in
the sewer pipe and in drop structures feeding it. High air flows have many negative impacts
including limiting the liquid flow, accumulating odorous air that requires exhaust and treatment
using air treatment facilities (ATFs) at various locations, and in extreme cases causing high
pressure air pockets that can cause structural damage due to pressure alone.
The design team developed strategies to reduce those negative impacts by limiting the volume of
air entering and conveyed in the tunnel. This project is believed to be the first to use these
strategies for a sewer tunnel of this size. The paper also discusses alternative treatment
technologies for exhaust air.


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Posted: May 20th, 2011 | Filed under: >1M, Waste Water Treatment | Tags: , , , , | No Comments »

TANSTAAFL: The ESCO Energy Optimization Process at 4 WWTPS

Washington Suburban Sanitary Commission (WSSC)
Laurel, Maryland

The Washington Suburban Sanitary Commission (WSSC) serves 1.8 million residents with water
and wastewater service with 2 surface water treatment facilities and 5 wastewater treatment
plants. In an effort to reduce operating costs and encourage sustainable practices the
Commission entered into a series of agreements with an Energy Services Company (ESCO) to
perform Energy Performing Contracts (EPCs). These alternative delivery projects involved theCost
Commission conducting upgrades to water and wastewater treatment facilities based on
guarantees of reduced operating expenditures.
In this project delivery and financing method, the ESCO in conjunction with the Commission
and the owners engineer conducted preliminary evaluations of treatment processes in an effort to
identify opportunities for reduction in operating expenses (power consumption, demand
management, solids disposal and fuel usage, based on a 15 year payback period. Upon
agreement between the owner and the ESCO as to the process improvement, construction cost
and reduction in operating costs, the owner and ESCO entered in an agreement whereby the
ESCO designed and constructed the improvement (under a modified design-build process) and
the ESCO guaranteed the projected operations savings for a 15 year period.
The first series of project involved the expenditure of $10.2 M in construction and design cost
with a guaranteed annual savings of $700,000 per year. In the first two years of operation, these
projects have saved $1,500,000 per year. While these figures indicate that the Commission has
been able to have its cake and eat it too, “There ain’t no such thing as a free lunch”
(TANSTAFL)”. The process and implementation of these projects demonstrated a number of
lessons to the Commission in how to conduct the initial evaluation, design, construction and
verification of energy savings. This paper will detail the challenges and lessons learned from the
ESCO process and demonstrate the path to success for future ESCO projects.
The process demonstrated the importance of well defined and consistent design standard,
particularly for instrumentation and control, electrical and HVAC systems. The Commission
was challenged with developing and writing appropriate contractual terms at the preliminary
design stage, as that is stage at which the project cost is established and requirements for
equipment are developed. In addition, the Commission was challenged with balancing the
desires and requirements of multiple groups including operations, engineering, finance, and
power management. The paper will present examples of each of the challenges, along with solutions to the challenges that allow the Commission to continue with this project delivery
method with greater success.


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Posted: May 20th, 2011 | Filed under: >1M, Sanitary Sewer, Stormwater, Waste Water Treatment, Water Treatment | Tags: , , , , , , , , | No Comments »