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| Monica, Chloe |
Monica: Would you describe the CSDOC operations?
Chloe: CSDOC owns and operates two large wastewater treatment
plants. Reclamation Plant No. 1 in Fountain Valley treats approximately
80 million gallons per day (MGD) of sewage. Treatment Plant No.
2 in Huntington Beach treats about 150 MGD. Both plants are located
in affluent residential neighborhoods and encompass state of the
art odor control technology.
Monica: How many years has CSDOC used chlorine for odor control?
Chloe: CSDOC has been using chlorine gas for many years now.
We have bulk chlorine stations at both plants, and also use a
lot of ton cylinders. Our chlorine usage was more than 10 tons
per day. Nearly all of the chlorine was used in prechlorination
for hydrogen sulfide control, since disinfection is not needed
except on an emergency basis. Some chlorine and bleach are used
in the odor scrubber towers.
Monica: What are the main factors that made you look at alternatives to chlorine?
Chloe: Our chlorine station at Plant No. 2 is old. We would have
to build a new station. This would be very expensive, perhaps
several million dollars, and would need total containment with
emergency scrubbing. Also chlorine is on the list of EPA hazardous
substances and we have to do an RMPP (Risk Management Prevention
Plan) if we are going to keep it.
Monica: Why peroxide?
Chloe: In 1982, we did a study. Chlorine was found to be the most
cost effective, but hydrogen peroxide was effective, too. That's
why we decided to try out peroxide again, and also peroxide is
environmentally friendly. We know that if we are going to go with
ferric chloride, we are still putting chemicals in the environment. So,
peroxide is the best alternative.
Monica: Please discuss the peroxide demonstration. Where did you add the hydrogen peroxide, and what control strategy did you use?
Chloe: We did the peroxide demonstration in May/June of last year at Plant No. 2. First, we did reaction studies to see how fast the hydrogen peroxide would react. Then, we set up dosing units to add peroxide to the five trunklines coming into the plant. The units were all located inside plant boundaries, so that it would prevent any public nuisance and protect public safety.
The units were set up on timeclock control to closely follow
the diurnal sulfide loadings coming into the plant. We did a lot
of test work, and during the demonstration period we were able
to optimize peroxide dosages down to approximately 700 gallons per
day, which represented about 1.5 parts of peroxide per part of
hydrogen sulfide. At this dose, we met all our objectives on hydrogen
sulfide levels.
Monica: So, the results must have been good. You have converted to peroxide at both plants?
Chloe: Yes, the results were excellent. Peroxide worked well, and the cost was very reasonable. On a straight chemical cost comparison, the hydrogen peroxide was slightly more, but with maintenance costs included, direct costs for peroxide were about the same or less than chlorine. This was based on our cost for chlorine, which at the time of the study was $247 per ton. And so, this gave us the chance to begin to eliminate gaseous chlorine.
We made a decision to go with peroxide as quickly as possible
at both plants using temporary systems at first. We are working
with our engineering consultants on the permanent peroxide systems
and the elimination of chlorine from both our facilities.
Monica: When did you start up fulltime on peroxide?
Chloe: We started up fulltime on peroxide at Plant No. 2 in October
last year, and at Plant No. 1 in December. Incidentally, since
we started up at Plant No. 2 we have been able to further optimize
the ration to 1:1, which further reduces the cost. And since our
chlorine price went up to $408 per ton in November, you can see
that we are very happy with peroxide. It is saving us a lot of money.
At Plant No. 1, the savings are not as great, but still significant
with the high price of chlorine. Our ratios are 3:1 to 4:1 at Plant
No. 1, where we lose some efficiency due to a very light loading.
Monica: What about the peroxide trials on the scrubbers?
Chloe: We also use 10 ft. diameter, packed tower scrubbers for odor control. They were originally designed for caustic alone, but because of Aqmd requirements, we add chlorine to oxidize H2S. We started using bleach, but bleach is quite expensive. So, in looking for another alternative we decided to try peroxide.
In our test work, we found that the performance of peroxide
was comparable to bleach. Overall the H2S reduction in air levels
was 98.9 percent and peroxide was cheaper to operate and eliminated
chlorine emissions. The latter may be important for future AQMD
requirements.
Monica: So, are you are going to use peroxide in the scrubbers?
Chloe: We have already started. At Plant No. 1 we are quite happy with peroxide at the headworks scrubbers. The results are quite good at low usage levels. At Plant No. 2, we are just setting up to test the headworks and trunkline scrubbers, as well as the whole north complex which is another 8 scrubbers. These will all soon be on-line with peroxide using temporary equipment.
We are also doing some test work at Plant No. 2 using a new
peroxide controller to automate the peroxide addition to the scrubbers.
So far it look promising.
Monica: How did the operations staff react to the transition from chlorine to peroxide?
Chloe: The staff were very happy with the safety aspects, because
it got them away from chlorine, which is a very dangerous gas.
It is much easier to operate a peroxide dosing system than a chlorine
dosing system. It is a liquid and has very simple and safe equipment.
That's what made them so happy. And also that the results were
comparable to chlorine.
Monica: Please comment on other benefits of using peroxide versus chlorine equipment?
Chloe: Operation and maintenance is more reliable than the chlorine
gas system. The cost is much lower, and the safety training requirement
is much less. Even with spilled peroxide you don't get into a
soil contamination problem because peroxide decomposes into water
and oxygen. But the major benefit with the switch away from chlorine
has been the improvement in staff and public safety.
Monica: What about liability, and risk management programs?
Chloe: We do not have to produce an RMPP, since 50% hydrogen
peroxide is not on the list of EPA hazardous chemicals and chlorine
is. Additionally, our liability insurance also went down dramatically.
These both represent major cost savings for us.
Monica: Any comments on the design of permanent systems?
Chloe: We are in the process of designing and building permanent
systems, which means that CSDOC is converting to hydrogen peroxide
usage at it's plants. Definitely to replace prechlorination. There
is still some question about the scrubbers, where trials are still
on-going.
Monica: Would you recommend hydrogen peroxide to others?
Chloe: For our application, peroxide works very well. So of course we would recommend
others to test H2O2. Actually, I have already had a number of enquires
from other cities and civil agencies.
For more information, please see the article in the CWPCA Bulletin (Winter Edition, 1994) entitled
"Evaluation of Chlorine Replacement Chemicals", by Chloe Dao.
 
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