Current News

Rocky Mount, North Carolina

Old oxygen generators might last forever but…

Thirty years ago, when the Tar River Regional Wastewater Treatment Plant in Rocky Mount, NC was new, it’s OASES secondary system had a state-of-the-art 50 ton per day (TPD) cryogenic oxygen generator to supply oxygen for its BNR secondary and ozone disinfection systems.  That cryogenic plant is still functional today; but at a cost.  In 2011, DWG ASSOCIATES and The Wooten Company (Raleigh, NC) looked at the efficiency of the cryogenic plant relative to current state-of-the-art oxygen generators.  That analysis indicated that there was considerable operating dollars to be saved by replacing the old oxygen generator with a new technology.  DWG ASSOCIATES and Wooten subsequently prepared specifications and a new, state-of-the-art AirSep Corp. Vacuum Pressure Swing Adsorption (VPSA) oxygen generator was installed.  The cryogenic oxygen generator was shutdown.  Estimated energy savings just for oxygen production with the new VPSA were projected to be $200,000 annually.  The new VPSA was started in January, 2013, and after 5 years of actual operation the energy reduction results are in.  "The new VPSA system is costing us $345/day for electricity, compared to more than $1,000/day for the old cryo plant," says now retired superintentent of wastewater treatment Kirk Bass.  The actual operating saving therefore is approximately $50,000/year more than initially projected.  Bass went on to say, "This [investment] has not only paid off, it has done so as quickly as the engineers promised."

Western Lake Superior Sanitary District, Duluth, Minnesota

Equipment upgrades can help you sleep at night…

Thirty/forty years is really an eternity in the life of a wastewater treatment plant.  The changes in service area, customer base, wastewater characteristics, or plant personnel during that time can significantly influence plant efficiency.  In the case of personnel, changes can also cause angst for plant management.  The Western Lake Superior Sanitary District (WLSSD) in Duluth, MN has recently been looking at the potential future changes they might expect for many of these parameters in the coming years.  The U.S Pulp & Paper industry (a large contributor to the plant) is waning.  Some critical senior plant personnel are nearing retirement age.  And most of the secondary equipment is nearing 40 years of age.  What to do?  DWG ASSOCIATES, in conjunction with Donohue & Associates (Donohue, Sheboygan, WI), was asked to evaluate the current condition of the UNOX System equipment at the WLSSD plant and recommend a cost effective path forward.  The existing UNOX System consists of 4 aeration trains of 4 stages each with an oxygen supply system of two 40 TPD cryogenic (cryo) oxygen generators.  We quickly determined that both the aeration system and oxygen generators were in good shape due to exceptional maintenance.  The aeration system was appropriately sized for current conditions, had considerable remaining life, and could easily be modified to handle changed future conditions should they occur.  So our concerns centered on the oxygen supply system.  What would it cost to upgrade the existing system to last another 20 years?  Could it be configured to operate efficiently should future plant loads decrease significantly?  How does the existing system compare from an operations and maintenance standpoint with newer technologies?  To address these questions, DWG ASSOCIATES and Donohue developed a financial model to account for WLSSD's identified potential future scenarios.  During scenario analysis it became obvious that 3rd party cryo plant operator assistance and training availability in the future was of critical importance to WLSSD because of impending personnel retirements.  Our financial model allowed for consideration of all potential future operating scenarios, including operator assistance and training costs.  Given the scenarios considered, our analysis indicated that the most cost effective path forward was to replace the existing cryo units with new state-of-the-art, fully automatic, less energy intensive Vacuum Pressure Swing Adsorption (VPSA) oxygen generators.  The VPSA's automatic operation and remote monitoring capabilities virtually eliminates future operator assistance & training worries and costs.  That means sound sleeping for management.  Specification development for the new oxygen generation system is in progress.

East Bay MUD (Oakland, California)/Louisville MSD (Kentucky)

Energy audits are a lot of work but…

Working with HDR Engineering, DWG ASSOCIATES conducted comprehensive energy audits of both East Bay’s Main Wastewater Treatment Plant (MWWTP) in Oakland, CA and Louisville’s Morris Forman Water Quality Treatment Center UNOX Systems.  Connected load and current operating philosophy were determined through detailed discussions with the operations staffs.  Using the prevailing power cost schedules for each plant, plant specific power saving and load shedding modes of operation were defined.  The capital costs of energy saving upgrades were established and a net present value-type analysis was used to identify the most attractive energy saving and/or load shedding modes of operation for each plant.  Approximately $500,000 in potential annual electric energy savings for just the East Bay UNOX System have been identified to date.  For the entire plant, total identified MWWTP energy reductions are currently resulting in annual operating cost savings approaching $3,000,000; which, in 2012, helped the MWWTP become the first wastewater treatment plant in North America to produce more renewable energy onsite than is consumed during normal operatation of the entire plant.  Similarly, approximately $300,000 in annual electical savings were identified (and are currently being realized) for just the Morris Forman UNOX System.  Total, entire plant Morris Forman energy savings were approximately $1,100,000 annually.  And most of the Morris Forman savings required little or no capital investment to capture.

South Essex Sewerage District, Salem, Massachusetts

How to sequentially upgrade to get ready for the coming 25 years…

The South Essex plant's UNOX System equipment is running as close to flawlessly as the staff can expect.  But the plant is approaching 25 years of age.  Plant management contracted with DWG ASSOCIATES to evaluate and quantify equipment replacement or refurbishment approaches that would (1) correct longstanding original design flaws and/or (2) provide cost effective methods to upgrade plant equipment to yield another 25 years of plant life.  DWG ASSOCIATES completed the entire plant evaluation in 2015.  Recommendations ranged from immediate fixes that would improve and ensure long term operating efficiency to a non-budget busting sequential equipment replacement/refurbishment schedule that would upgrade overall plant operating efficiency while positioning the plant for 25 more years of operation with minimal maintenance expenditures.  The sequential schedule will ensure that upgrade expenditures will only be made when justified by (1) energy efficiency improvements or (2) escalating maintenance expenditures associated with impending equipment failure.  The South Essex plant can now move forward knowing what areas of their UNOX System need replacing or refurbishiment each year.

Cedar Rapids, Iowa

Bring your oxygen generator into the 21st century, as well as into your SCADA system…

Because of excellent maintenance, the Cedar Rapids Cryogenic plant was still robust and producing oxygen almost as efficiently as when it was new; 35 years ago.  But the original pneumatic instrumentation system was antiquated, hard to maintain, and not a part of the wastewater plant’s existing SCADA system.  In addition, the old water bath vaporizers for the backup liquid oxygen (LOX) supply system were expensive to operate and some of the cryo plant’s wear items (e.g., the reversing heat exchanger switching valves, etc.) were getting a little "long in the tooth."  Therefore, the upgrade of the Cedar Rapids cryo, which was completed in 2014, included digitization of the control instrumentation system, incorporating the cryo's new control instrumentation into the wastewater plant’s SCADA system, replacement of the old plug-type reversing heat exchanger switching valves with high-cycle butterfly valves, and replacing the LOX water bath vaporizers with atmospheric vaporizers.  The upgraded plant is now on-line, saving considerable maintenance costs, and ready for the next 25 years of operation.

Oxygen Supply System Upgrades

If you’re wondering how much longer your original PSA or Cryo plant will last…

The energy efficiencies of all technologies change with time.  For HPO systems, oxygen supply technologies have changed considerably over the last 20 years.  VPSA/VSA and LOX supply systems have proven to be cost effective alternatives to the PSA and cryo oxygen generators originally installed at most high-purity oxygen plants.  VPSA/VSA systems, in particular, are seeing significant efficiency improvements as vendors’ R & D money continues to be expended on this state-of-the-art technology.  Detailed economic evaluations have recently shown it’s cost justified to replace old, inefficient oxygen generation equipment at Orange County (CA), Rocky Mount (NC), Yuba City (CA), Duluth (MN), and Louisville; all of which will replace their original oxygen supply systems.  DWG ASSOCIATES’ familiarity with the newer technologies and experience with the economics and efficiencies of these upgrades will ensure you of the most appropriate and cost effective upgrade for your future needs.  And if your future includes new oxygen production equipment, don’t just assume that your old equipment is worthless.  There is a small but existent market for used oxygen generators (both PSA and cryo) and LOX storage equipment.  DWG ASSOCIATES knows this secondary oxygen plant market well.  So if you have (or anticipate having) used oxygen supply equipment, let DWG ASSOCIATES know.  In most cases we can investigate at no cost to you whether there’s a customer other than the scrap yard for your old equipment.  But please be aware, the sooner we know your equipment is becoming available the more chance we have of being successful finding someone that can utilize it.