29 3/3 /JP Readily available supply of H202 at most mills, coupled with application

knowledge, can resolve many temporary and seasonal problems

in Solving Mill Environmental Problems ORE THAN 50% OF ALL HY- drogen peroxide (H,O,) manufactured in North America is consumed by

the pulp and paper industry. One prima- ry consideration for its use is the chemi- cal’s environmentally compatible by- products-water and oxygen. These byproducts make hydrogen peroxide an excellent agent for pollution prevention.

Pulp and paper manufacturers were among the first to recognize the impor- tance of in-process pollution preven- tion. Pollution prevention was found to be cost-effective and produce greater levels of pollution control. On the oth- er hand, end-of-the-pipe treatment of large volumes of wastewater generated from the production of pulp and paper became cost-prohibitive as effluent reg ulations tightened.

Pollution prevention is the major driving force today in the growth of hy- drogen peroxide demand world-wide. This demand parallels the growth in the number of federal, state, and local envi- ronmental regulations (Figure 1) .

As more and more pulp and paper mills utilize hydrogen peroxide in their production processes, they are also gaining the capability to treat environ-

mental problems in a simple and cost- effective manner. Many common envi- ronmental problems are temporary or seasonal, so that the installation of per- manent treatment systems becomes an unwanted capital expense.

USE OF HZOZ TECHNOLOGIES. Hydrogen peroxide is a versatile chemical. It can be used as either an oxidant or a reduc- tant. It is also a convenient source of dissolved oxygen. Hydrogen peroxide has demonstrated biocidal activity, al- though its use in this application is limited, since it is not currently regis-

FIGURE 1: Comparison of the total North American HP, market vs new federal, state. and local environmental laws.

tered by EPA as a biocide. The most im- portant considerations for effectively implementing hydrogen peroxide tech- nologies are as follows:

Proper identification of the envi- ronmental problem System compatibility Reaction chemistry (stoichiometry

Logistics. Table 1 shows the stoichiometry and

kinetics commonly observed when hy- drogen peroxide reacts with common pollutants.

NUISANCE ODOR CONTROL. One of the most aggravating environmental prob- lems a pulp and paper mill deals with can be nuisance odor. While a mill’s employees and neighbors are often ac- customed to the smell of pulp and pa- per manufacturing, an unexpected change in the odor can cause alarm and affect mill public relations.

Hydrogen sulfide is the most com- mon nuisance odor associated with pulp and paper mills. With a threshold odor of only 0.4 ppb, it has an easily recognizable and offensive rotten egg odor. Hydrogen sulfide is also a very corrosive gas. When adsorbed onto sur- faces, it combines with moisture and forms sulfuric acid.

Hydrogen sulfide odors are released as nonpoint source gaseous emissions. Wastewater clarifiers, gravity thicken- ers, and sludge dewatering units are

r sources. In these treatment units, hy- drogen sulfide can be generated in a rel- atively small area but can propagate its odorous effect over a large area. Aerated stabilization basins (ASBs), lagoons, and holding ponds occupy larger areas. These systems spread the odor nuisance of hydrogen sulfide over even greater distances.

One large southeastern pulp and pa- per mill dredged anaerobic sludge from its settling ponds. The dredged sludge was creating airborne hydrogen sulfide

and kinetics)

NOVEMBER 1994 P U L P 8 P A P E R 111

I i I

TABLE 1 : Hydrogen peroxide reaction chemistry.

Theoretical weight ratio, Reaction H,O, : pollutant 100% basis time Catalysts

I Amines Alkaline 0.4 to 0.8:l Minutes to hours None I

n cyanides cannot

1 ~ I

levels above 120 ppm as it entered the sludge dew;rtcring system After experi- menting with varions treatment tech- nologies. 0 68 gpm of 50% hydrogen peroxide was injected into the influent of the niill’\ cvclone prior to the sludge press drwrering unit This effectively controlled the hydrogen sulfide levels to the target level of lers than 20 ppm.

POINT SOURCE GASEOUS EMISSIONS. Total reduced sulfur (TRS), NOx, and SOU ;ire common air pollutants from pulp and paper mills The point sources for these enii,\ions arc lime kilns, re- covery boiler\. and gas scrubbers. The use o F hydrogen peroxide for control- ling SOU and ‘VOX is limited due to the nrrd to recover usrablc strengths of by- prodwt sulfuric or nitric acid Normal- ly the lcvelr of SOX and NOx from pulp and paper point sotirccs are too low to

\

from a spray bar system onto the lime mud filter during periods of high TRS loadings wils sufficient to maintain the TRS emissions below 20 ppm. The hydro- gen peroxide reduced the TRS fraction, which evolved from the lime cake in the cold end of the kiln (Figure 2). It did not reduce the noncondensible TRS fraction injected into the hot end of the kiln from the recovery boiler.

TREATING WATER. Both process water and wastewater problems can be treated with hydrogen peroxide. As mills begin to eliminate waste streams and recycle wastewater, the unique characteristic of treating problems with hydrogen peroxide becomes clear. Hydrogen peroxide produces water and oxygen as its residuals. Hydrogen peroxide treatment addresses such problems as oxygen demand, sludge bulking, TOC

The BOD and COD of a wastewater can often be significantly reduced by removing this immediate oxygen de- mand via oxidation with hydrogen per- oxide. After the immediate oxygen de- mand is satisfied, any residual hydrogen peroxide decomposes to form water and oxygen. This residual oxygen by- product is useful in boosting the dis- solved oxygen (DO) of the wastewater. The use of hydrogen peroxide to add DO to a wastewater is referred to as oxy- gen supplementation.

A southwestern pulp and paper mill recently experienced a black liquor spill that caused its effluent BOD to ap- proach the permit level. Hydrogen per- oxide was added to oxidize the reduced species from the black liquor spill. The addition of 1 . 1 gpm of 50% hydrogen peroxide into the primary clarifier was sufficient to keep the system in compli-

mit

Hvdrogm peroxide can be used ef- fectivrly to control TRS point source rmisions from gas scrubbers and lime kilns Another air polliltant that some mills cupvricwce i s chlorine gas Hydro- gen pcrourdc can be wed effectively in a n alk;ilinc gas scriihhrr to convert scriibherl hypochlorite ions to oxygen gas and chloride ions

A sortthrrn pulp and paprr mill had d i ffi cit Ity m:r inra ini ng the TRS rmissi ons from it5 lime kilns below 20 ppm Apply- ing 3 gal/hour of 50%) hydrogen peroxide

removal, dechlorination, and metals removal.

OXYGEN DEMAND: BOD, COD, AND DO. The use of uncatalyzed hydrogen perox- ide to oxidize the organic fraction of a wastewater’s BOD or COD is hindered by slow-reaction kinetics. However, when it is applied to wastewater systems, it does immediately react with reduced inorganic species such as sulfides. These reduced species represent the immediate oxygen demand of a wastewater.

SLUDGE BULKING CONTROL. Activated sludge treatment (AST) of pulp and pa- per wastewater is subject to occasional upsets that stress the bacterial popula- tions present in the sludge. Under these stressed conditions, filamentous bacte- ria tend to thrive and normal activated sludge bacterial populations do not.

This population shift in the sludge causes it to settle slower than the de- signed settling rate of the existing clari- fier system used to recycle and waste

112 P U L P 8 P A P E R NOVEMBER 1994

sludge. The result is that sludge passes over the weirs of the clarifier, which can quickly cause effluent permit violations.

Hydrogen peroxide inhibits the growth of some forms of filamentous bacteria and, when properly applied, promotes a population shift back to the normal AST bacteria. However, hy- drogen peroxide can exert toxic ef- fects on normal activated sludge when improperly applied. The toxicity of hydrogen peroxide is both time and concentration dependent. When us- ing this technology, care must be giv- en to avoid harmful effects on the acti- vated sludge.

A midwestern pulp and paper mill was experiencing sludge bulking prob- lems due to a proliferation of filamen- tous bacteria. A dose of 60 ppm of h y drogen peroxide into the return sludge line produced a 20-ppm residual per- oxide level in the activated sludge ba- sin. This dose of hydrogen peroxide was sufficient to retum the activated sludge to its normal operating conditions with- in a few days.

ORGANICS, TOXICITY, COLOR REMOVAL. Certain organic substances can increase the toxicity and color of an effluent. These substances may also be refractory to standard wastewater treatment sys- tems. Catalyzed hydrogen peroxide can be an effective method of solving the problems presented by specific organic substances.

Referred to as Advanced Oxidation Processes (AOP) , catalyzed hydrogen peroxide results in the formation of the highly reactive hydroxyl radical. Since the hydroxyl radical is a powerful non- selective oxidant, hydrogen peroxide

dosing is usually based on the COD or Total Organic Carbon (TOC) instead of the problem-causing organic species. Ozone, ultraviolet light, and iron are three of the most common methods of catalyzation. Iron-catalyzed hydrogen peroxide is referred to as Fenton’s treat- ment and is the easiest of the three to apply. Fenton’s treatment has two limi- tations-a required acidic reaction pH (3 to 4) and the formation of byproduct iron sludge.

A northwestern pulp and paper com- pany diverted process upset wastewater into a 10-million-gal holding pond. Studies showed that the wastewater in the holding pond was extremely inhibi- tory to the biomass in the activated sludge-based treatment system. The TOC and toxicity of the wastewater were measured at 300 ppm and 15.4% (EC5, at 15 min), respectively. A Fen- ton’s treatment of the holding pond was conducted by dosing approximately 4: 1 H,O,:TOC w/w ratio with 125 ppm of iron as Fe at pH 3 to 5. After 96 hours, the TOC had been reduced by 74%, and the toxicity had improved tenfold. The wastewater was then pumped into the primary clarifier of the mill’s wastewater treatment system without any deleterious effects on the system.

DECHLORINATION. In chloralkali plants, H,OZ can serve an important role as a dechlorinating agent. Waste caustic streams from scrubbers, as well as exist- ing plant effluent, must be treated to meet existing NPDES permits.

In the presence of a strong oxidizing agent such as chlorine, peroxide can ef- fectively serve as a reducing agent. At al- kaline pHs, H,O, reacts with the hypo-

chlorite ion to form oxygen and the chloride ion. Hydrogen peroxide has the advantage of leaving no sulfate residual.

CONCLUSION. The increased use of hy- drogen peroxide in the manufacture of pulp and paper has expanded the op- portunities for mills to utilize its capa- bilities as an environmental treatment chemical. A readily available supply of hydrogen peroxide, coupled with the appropriate application knowledge, can result in effective resolution of many temporary or seasonal environmental problems. The trend toward total clo- sure of water circuits used in pulp and paper mills will also make the use of hy- drogen peroxide attractive as its by- products are merely water and oxygen.

Bottom-unloading isocontainers that serve as rapidly deployable temporary bulk storage systems for hydrogen perox- ide make utilization easier. These systems are useful to mills that are not currently using hydrogen peroxide, or that are un- able to dose the hydrogen peroxide from their existing storage facilities. Isocon- tainers can be shipped within 24 hours to respond to emergency situations requir- ing immediate attention.

STEVE ROBINSON i s senior customer support representative, Solvay Interox, Houston, Texas.

FIGURE 2: Applying hydrogen peroxide onto a lime mud filter during periods of high TRS loadings helped a southern pulp and DaDer mill maintain TRS emissions from its lime kilns below 20 DDm.

NOVEMBER 1994 P U L P 8 P A P E R 115

ULP & PAPER FORECASTER shows P you the next five years The rapid recovery in linerboard and market pulp during 1994 has moved demand and pricing to record levels. As other areas of the industry improve, the question now is: how long can the strong current markets be sustained? Will a new round of capital spending begin during years of peak earnings in 1996-97? When will a downturn hit?

You must start planning now to fully benefit from this projected upswing. That's why PULP & PAPER FORECASTER will release its special FIVE-YEAR

report early this year-as the November /December 1994 issue.

Even if you're not a

OUTLOOK (1995-1999)

Operating rates

New supply (demand) Import Prices

FORECASTER subscriber, /n thisspaidisw, theannual you can take advantage ~~~~~~~~~~

of this invaluable tool for within the induty.

long-term planning, budgeting, and forecasting within the North American market for all key pulp, paper and paperboard grades.

ow long will the recovery last? H FIVE-YEAR OUTLOOK (1995-1999) focuses on where and how long the recovery cycle will he in U.S. and Canadian pulp, paper and paperboard grade sectors. It details which sectors will improve the most and which will remain poor performers.

FIVE-YEAR OUTLOOK (1995-1999) will help y@

and pricing. Key variables for each major grade are forecast for 1995-1999, as well as tracked for the present year and the two previous years. Easy-to-read tables and charts show this data for:

Important t m d s within eachgrade segment are clearly iUustrated and discussed

';(folding, kntainerboard, ohers); and chehical paper- grade market Pulp.

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ou could use a look into the Y future ... Are you a producer ofpaper or paperboard? You'll find in-depth analyses and discussions of operating rates, demand, and pricing trends essential

budgeting.

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re you interested in the next five A years? PULP & PAPER FORECASTER'S FIVE-YEAR OUTLOOK

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