FOG – Figuring Out Good Solution to Fats, Oils and Grease in Advanced Wastewater Treatment Systems
Miami-Dade Water and Sewer Department (MDWASD)Miami, Florida
The Miami-Dade Water and Sewer Department (MDWASD) is implementing a major upgrade
program at the South District WWTP in response to capacity upgrade requirements, regulatory
mandates and commitments to optimize water resources. In the recent past, MDWASD initiated
implementation of one of the largest High Level Disinfection Programs in the country (285-mgd
peak hour). In general, wastewater treatment facilities deal with a large number of operating and
maintenance concerns, not the least of which is Figuring Out Good solutions to Fats, Oils and
Grease (FOG) problems. The MDWASD SDWWTP has unique FOG problems including typical
clogging and aesthetics concerns as well as the presence of very fine and dispersed FOG in its
secondary effluent. The chemical composition and characteristics of FOG result in an inherent
difficulty with its treatment and its impacts to WWTP’s, especially for effluent polishing (filtration
and chlorination) and advanced treatment with membranes. Based upon significant concerns
for impacts of Fats, Oils and Grease levels on the existing secondary WWTP and concerns for
clogging of 30 planned, large deep bed filters with a capacity rating of 285 mgd, an intensive
field sampling, testing and evaluation program for FOG sources and treatment options was completed.
Results of this evaluation were presented at WEFTEC 2005, and are hereinafter referred
to as “FOG Part 1”. Under FOG Part 1, FOG clogging of main WWTP pipelines, and existing
continuous backwash filters for effluent reuse onsite resulted in a detailed sampling and analytical
program that reviewed and characterized FOG sources. FOG characterization in the septage,
leachate and influent sources to the WWTP were addressed. Based upon this characterization,
influent sources and clarifier scum removal were identified as key areas of focus in the WWTP.
Related improvements to these key areas including the addition of a Septage Receiving and
Treatment System at the front end of the WWTP, improvements to FOG removal at the secondary
clarifiers, direct removal or vacuum removal of FOG from the wastewater flow stream, additional
separation and concentration of FOG that is removed from the wastewater flow, and the
addition of a select residuals management system for mixing, handling and disposal of FOG
along with other residuals (grit, screenings, etc) were recommended at this secondary plant in
preparation for the addition of an HLD system. These improvements are currently under construction
with a planned completion of around fall of 2011.
Concurrent with the HLD and FOG upgrades, MDWASD is implementing one of the country’s
largest water reclamation facilities – 21-mgd treatment, delivery of 18.6 mgd of finished product
water, used for augmentation of Miami-Dade County’s drinking water supply through groundwater
recharge. Thus, potential impacts of FOG on advanced treatment membrane processes- microfiltration
(MF) and reverse osmosis (RO) needed to be investigated due to potentially significant
impacts to capital costs, operation and maintenance and downtime that could limit capability
for reliably providing the necessary quantities of water to augment drinking water supplies in this
region.
An advanced treatment pilot system was constructed and tested using secondary effluent at the
SDWWTP. The pilot system consisted of deep bed filters and high level disinfection (HLD) with
chlorine solution, plus advanced wastewater treatment processes including MF, RO, ion exchange
(IX) and ultraviolet disinfection with advanced oxidation (UV-A). The pilot was utilized
to demonstrate treatment capability of the proposed process units, define design criteria, and better
understand operational and maintenance issues and potential concerns such as FOG.
At the time of the pilot testing, the majority of the upgrades for improved FOG removal from the
secondary process were still under construction, and therefore, the reclamation pilot was tested
under “worst-case” conditions from a FOG perspective. FOG influent and effluent data were collected
and analyzed. The pilot deep bed filter system removed FOG from the secondary process -
FOG levels of roughly 1 to 11 mg/l were reduced to roughly 1 to 3 mg/l. Also, visual observations
indicate that this removal of FOG at the filters did not impact the filter media. However,
due to the nature of the fine FOG particles at SDWWTP, FOG downstream of the filters still
needed to be addressed from the perspective of potential accumulation on the membranes. Regarding
potential impacts of FOG on the membranes, specific flux plotted versus run time for the
RO membranes shows relatively stable specific flux values, with gradual decline over a duration
of about 3 months. A cleaning cycle then was implemented for collection of “cleanability” data.
Subsequent to cleaning, the data generally show an increase in specific flux to roughly the initial
specific flux rate of the membranes which supports that FOG did not accumulate on the membranes.
Similarly, Permeate Conductivity Versus Run Time and showing Differential Pressure
Versus Run Time indicate relatively stable data over roughly 3 months. In general, pilot testing
supports that FOG, which has been a concern for the South District Secondary WWTP, is not
anticipated to impact the advanced treatment processes for production of reclaimed water that
will supplement the Miami-Dade County drinking water supply through groundwater recharging.
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Posted: May 20th, 2011 | Filed under: >1M, Stormwater, Waste Water Treatment, Water Treatment | Tags: Advanced Wastewater, Cost Effective Alternative, Fats, Oils and Grease (FOG) Control, Optimize Water Resources, Reduced O&M Problems, Reduced Pipe Clogging | 1 Comment »