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SCMA Annual Conference & Expo “Membranes: Basics, Barriers, and Breakthroughs”

San Antonio, TX – Aug. 20 - 22, 2014

© SCMA

Joshua Berryhill, PE Enprotec / Hibbs & Todd, Inc. (eHT)

It is Time for MBR – A Comparison of MBR Vs. Traditional Wastewater Treatment

Technologies

© SCMA South Central Membrane Association 2 © SCMA

Discuss fundamentals of MBR

Discuss types of MBR systems

Compare MBR operation to existing technologies

Discuss piloting and design requirements

Discuss lessons learned from early MBR installations

Presentation Topics


Regulatory Requirements

Wastewater Treatment

Reviewed under §217.7(b)2 as innovative treatment techniques and exceptions to the Rules

Must meet site-specific performance requirements when used at WWTPs, in lieu of conventional WW treatment design, per §217.157

Does not require piloting of proposed MBR system, unless the proposed MBR system design criteria is more aggressive than the design limits allowed in §217.157

Fundamentals of MBR


Differences in Terminology for MBR MBR – Membrane Bioreactor

Membrane – Material where the lateral dimensions (length, width) are much greater than the material thickness

Conventional Filtration – Uses granular or cloth media

Filtrate – Filtered water from an MBR system

Conventional Filtration - Filter effluent

Concentrate – The waste stream from an MBR system

Conventional Filtration – Similar to backwash waste

Fundamentals of MBR


Differences in Terminology for Membranes Flux – A measure of the rate at which the filtrate passes through the membrane per unit of membrane surface area, expressed as gallons per square foot per day (gfd)

Conventional Filtration - Surface loading rate (gpm/sf)

Transmembrane Pressure (TMP) – Measurement of the force required to push/pull filtrate across a membrane surface

Conventional Filtration - Filter head loss

Fouling – Loss of performance due to suspended or dissolved material deposition on the membrane surface

Conventional Filtration – No similar concept

Fundamentals of MBR


Differences in Terminology for Membranes Recovery – Ratio of filtrate produced compared to the original feed water flow rate, expresses as a percentage

Conventional Filtration – Net water production

Reverse Filtration / Backpulse – Forcing filtrate back through the membrane to clean off the feed side of the membrane

Conventional Filtration – Filter backwash

Clean-In-Place (CIP) – Cleaning the membranes by soaking in chemical solutions while still inside the MBR basin

Conventional Filtration – No similar concept

Fundamentals of MBR


Fundamentals of MBR

Large Siliceous Particle (20 µm)

Microfiltration (0.1 µm) Ultrafiltration (0.04 µm)


Fundamentals of MBR

• Hollow Fiber Membrane

MBR Issues

Scum control

Pretreatment

Peak flows

Air scour (HP)

Membrane cleaning

Membrane replacement

Conventional Issues

Scum control

Sludge settleability

Weir cleaning

Filter cleaning

Filter replacement/maintenance


< 2.5

2.5 - 25

25 - 125

> 1,250

Total Installed Capacity MGD

250 – 1,250

Fundamentals of MBR


Worldwide MBR drivers

Data Sources: Investigation of MBR Effluent Water Quality and Technology – A Worldwide Survey (WRF-06-007) – MWH Main technical challenges of MBR – A survey of MBR users and suppliers – Santos et al, 2010

MBR technology challenges Fundamentals of MBR


Types of MBR Equipment

Manufacturer Membrane

Manufacturer

Membrane U.S. Experience

Type Pore Size (um)

Material No. Largest Longest

MGD Years

GE/Zenon Zenon 500C/D Hollow Fiber 0.04 PVDF 100+ 18

(12 in Texas) 19

Enviroquip Kubota Flat Sheet 0.4 (0.1) CPE 100+ 6

(3 in Texas) 11

Siemens Siemens Memcor Hollow Fiber 0.1 PVDF 35 3.5 8

Kruger Toray Flat Sheet 0.08 PVDF 8 1 6

Koch Koch Hollow Fiber 0.04 PVDF 8 3.4 2

Other manufacturers with limited U.S. experience: •Ovivo – Now Partnered with Microdyne •NoritXFlow •Westech – Partnered with Alfa Laval Membrane •Puron


Types of MBR Examples of Hollow Fiber MBR


Types of MBR Examples of Flat Sheet MBR


Types of MBR • Module → Cassette → MBR

• Flat Sheet Membrane


Comparison of Membrane Operation Basic differences in operating principles.

Conventional plants (those with final clarifiers) rely on final clarifiers to settle the solids from mixed liquor leaving clear effluent to flow from clarifier. Operators of WWTPs with final clarifiers must produce a sludge that will settle leaving behind clear effluent.

New MBR systems do not have final clarifiers (only early tertiary MBR systems). Process control related to making sludge settle goes away. No longer care if the sludge will settle. Process control shifts to maintaining nutrient removal treatment. Also now have effluent filtration. Well suited to plants with nutrient removal in their TPDES permit or Type I reuse needs.

Additional potential for potable reuse as well.


Comparison of Membrane Operation How are pretreatment requirements different for MBR treatment?

Fine screens and advanced grit removal are required for MBR plants to protect the membranes.

MBR plants are commonly used to provide nutrient removal. Nutrient balance becomes more of an issue if biological nutrient removal is required.


Comparison of Membrane Operation How are instrumentation requirements different for MBR treatment?

Instrumentation required to operate an MBR system is more complex than for conventional WWTPs.

Very little difference in instrumentation requirements for TPDES compliance verification.

Analytical procedures for permit compliance remains bench top analytical with an MBR plant as it does with a conventional WWTP with final clarifiers.


Comparison of Membrane Operation How are MBR membranes different from conventional filters in cleaning?

Membranes are cleaned in several ways. Additional chemicals are used in the cleaning process:

Routine short backwashes on regular intervals (every 15-30 minutes) using water and air pulses. Membrane remains in normal service.

Weekly mini-CIPs (maintenance cleans) using low pH (acid) and/or chlorine (hypochlorite). Membrane out of service for short period.

Long-CIPs using low pH (acid), high pH (caustic) and chlorine (hypochlorite). May also use neutralizing chemicals to neutralize chlorine and low/high pH (monthly). Membrane out of service for 1-2 days.


Comparison of Membrane Operation How is equipment operating life different for membrane systems?

Membrane life expectancy currently ranges from 5-10 years (several facilities in the US currently have a membrane life over 12 years). Issues that have the greatest effect on membrane life include:

Optimizing frequency and strength of mini- and long-CIPs

Maintaining a consistent feed water quality to the membranes

Exercise the membranes on a routine basis (ramp up to peak flow capacity regularly)

Dual media filter beds by comparison typically last about 10-20 years before needing to be rehabilitated.


Comparison of Membrane Operation How do membranes change operation of solids and waste stream handling?

MBR systems can be capable of meeting Class B treatment requirements, depending on SRT. SRTs above 14 days from the biological process can be considered aerobic digestion and meet vector attraction reduction requirements.

Use of MBR can potentially significantly reduce solids stabilization requirements.

Coordination with TCEQ to determine overall solids stabilization requirements for your MBR system is critical!


Comparison of Membrane Operation Monitoring and Reporting – Direct Integrity Test

No requirements (yet) from TCEQ on completing direct integrity tests for MBR systems.

A DIT requirement could potentially be added in the future, especially for planned direct or indirect potable reuse programs.

Identifying and planning for future treatment requirements is critical when considering the implementation of MBR!


Piloting and Design Requirements What is a pilot and why do we do it?

Why pilot?

Only to design around more aggressive criteria than that allowed by TCEQ under 30 TAC 217.

i.e. designing for MLSS above 10,000 mg/L in aeration basins or above 14,000 mg/L in MBR basins

30 TAC 217.157(c)(2)(D) requires that design values requested outside the range listed in 30 TAC 217.157 will require the completion of a pilot study to verify sustainability of the proposed design values


Piloting and Design Requirements How do membranes impact solids handling in wastewater processes?

Conventional Solids Handling

Secondary Clarification, RAS/WAS Pumping, Solids thickening, solids dewatering and disposal

Sludge in aeration basin – 2,000 – 4,000 mg/L MLVSS

MBR System Solids Handling

MBR, Waste solids from MBR basin, solids dewatering and disposal

Sludge in aeration basin – 8,000 – 20,000 mg/L MLVSS


Piloting and Design Requirements Processes Required for MBR System?

BNR Biological Process - Required to handle higher solids recycles from MBR

MLSS Transfer from Aeration Basins to MBR - Either by gravity (requires pumping of RAS) or pumping (allows gravity recycle of RAS)

MBR System

MBR filtrate pumping system

MBR backwash system

MBR RAS/WAS handling system

MBR air scour system

MBR chemical cleaning system


Lessons Learned from Early Installations Scum Control is Important

Initial MBR installations did not utilize any kind of scum control or scum removal method. MBR systems can operate above 10,000 mg/L MLSS, which increases the potential of scum formation.

New MBR designs utilize a skimming or spray method to remove scum from aeration basins and MBR basins.


Lessons Learned from Early Installations Effective Pretreatment is Critical!

Initial MBR installations utilized 3-6 mm screening pretreatment ahead of MBR systems, resulting in extensive buildup of debris on the membranes.

New MBR designs center around 3 mm maximum fine screens for flat sheet MBR and 2 mm maximum fine screens for hollow fiber MBR


Lessons Learned from Early Installations MBR Systems are Sensitive to Peak Flow

Initial MBR installations attempted to treat all incoming flow instantaneously, regardless of peaking factor. This resulted in reduced membrane life due to excessive wear and tear on the membrnes.

New MBR designs focus on a maximum peaking factor of 2:1 to regulate membrane wear and tear. Any wastewater system that sees dry weather or wet weather peaking factors in excess of 2:1 need to plan for implementing a flow equalization (EQ) system to divert, store and recycle excess flows when appropriate.


Lessons Learned from Early Installations Need for and Impact of MBR Air Scour System

Initial MBR installations attempted to minimize the air use for intermittent air scour of the membranes, due to its inherent high energy cost.

New MBR designs utilize more advanced and efficient air scour systems that significantly reduce power use. Power consumption for air scour has decreased by more than 50% over the past 10 years. New MBR designs can also take advantage of the extra DO in MBR RAS (typically 5-6 mg/L DO) to more efficiently design new process air blower systems, minimizing overall WWTP energy use.


Lessons Learned from Early Installations Need for and Impact of MBR Air Scour System

Aeration tubes replaced by LEAPmbr AT devices

One 3” air connection


Lessons Learned from Early Installations Risks of loss of MBR membrane capacity as a result of changing water conditions

Some systems have seen rapid (and sometimes irreversible) fouling of membranes as a result of deteriorating water quality.

Concentrated organics, increased bio-fouling, increased scaling potential, reduced effectiveness of mini- and long-CIPs

Trending MBR operational data is critical to determine patterns of increased fouling and reduced cleaning effectiveness on a daily, weekly, monthly, and annual basis!

Ongoing communication with the MBR manufacturer and the design engineer is key!


Lessons Learned from Early Installations Risks of loss of membrane capacity as a result of unchecked fouling

Some systems have seen rapid (and sometimes irreversible) fouling of MBR membranes as a result of unchecked fouling. CIPs and/or chemically enhanced backwashes were not completed because the TMP did not appear to require cleaning.

When running an MBR system under capacity, the effective TMP will be artificially low. True foulant testing should be completed when operating the MBR system at net production in order to accurately gauge fouling potential.

Trending MBR operational data (for net production periods, not just under low loading rates) is critical to determine patterns of increased fouling and reduced cleaning effectiveness on a daily, weekly, monthly, and annual basis! Ongoing communication with the MBR manufacturer and the design engineer is key!


Lessons Learned from Early Installations Membrane Life

Some systems have seen a membrane life of greater than 10 years, while other systems have seen a life of 5 years or less.

Biological fouling does not typically contribute to irreversible fouling for MBR. Inorganic scale fouling and fouling due to chemical addition (such as metal salts for P precipitation) are frequently the majority of the contribution to irreversible fouling and loss of permeability.

Trending MBR operational data is critical to determine patterns of increased fouling and reduced cleaning effectiveness on a daily, weekly, monthly, and annual basis!

Ongoing communication with the MBR manufacturer and the design engineer is key!

A typical MBR warranty ranges from 5-10 years, so utilities should budget for the next MBR membrane replacement on a 5-7 year basis.


Lessons Learned from Early Installations Membrane System Service Contracts

Most of the major MBR manufacturers offer an annual service contract. The intent of the service contract is to provide a quarterly, semi-annual or annual checkup of the membrane system to verify effectiveness of air scour, chemically enhanced backwashes, CIPs, etc.

Beneficial use of a service contract can lead to maintaining optimized cleaning and maintenance efforts of the MBR system, which can optimize membrane performance and increase membrane longevity.

Service contracts can range from low to fairly high cost (based on frequency of site visits included in the contract). Discussion of key contract goals with the MBR manufacturer and your design engineer is a must to custom-tailor a contract to your needs.


Summary

Why conventional ???

Capital expenditure ($M)

20 year life cycle cost ($M)

* Based on 5 MGD treatment capacity as compared to Conventional Secondary Treatment.


Thank you for your time!

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