22 Wastewater Management in the Solid W o o d and Board Products Industries: A Review
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WARREN S. THOMPSON Mississippi Forest Product Laboratory, P.O. Box 552, Mississippi State University, Miss. 39762 Concern over the deteriorating quality of the environment has focused world-wide attention on pollution in its various forms and on industry's contribution to this problem. Because of stringent legislation, the incentive to develop pollution abatement and control technology has perhaps been greater in the United States than in other countries in North America. Over 250 pieces of pollution legislation have been passed at state and federal levels since the early 1960's. Effluent guidelines for the timber products processing i n dustry have been developed by the United States Environmental Protection Agency (EPA) as part of an over-all pollution control program ordered by Congress in its 1972 Amendments to the Federal Water Pollution Control Act of 1965. This legislation has significance to the wood products industry in general, since the pollution problems that it addresses are essentially the same worldwide. This paper describes the pollution problems related to water in wood-based industries in the United States, summrizes current effluent standards as they apply to the industry, and discusses the technology available to meet these standards. Federal Effluent Standards Under the provisions of the 1972 Amendments to the Federal Water Quality Control Act, the U. S. Environmental Protection Agency i s required to develop effluent limitations for a l l indust r i a l point sources of discharge. Guidelines for the wood products processing industry have been promulgated. They identify in terms of the amounts of constituents and the characteristies of pollutants the degree of discharge reduction that must be achieved through the application of two levels of control and treatment designated as Level I Technology and Level II Technology. Level I Technology i s defined as the best practicable cont r o l technology currently available and must be achieved by a l l point sources of discharge by July 1, 1977. It i s based on the
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average e x i s t i n g performance by exenplary p l a n t s o f v a r i o u s s i z e s , ages, and types o f processes w i t h i n an i n d u s t r y . L e v e l I I Technology i s t h e best a v a i l a b l e technology e c o n o m i c a l l y a c h i e v a b l e and must be a t t a i n e d by a l l p o i n t sources by J u l y 1, 1983. Performance under t h i s l e v e l o f technology i s based on t h e best c o n t r o l and treatment technology e x i s t i n g i n an i n d u s t r y o r which i s t r a n s f e r a b l e from another i n d u s t r y . In t h e development o f e f f l u e n t g u i d e l i n e s , each i n d u s t r y was s u b d i v i d e d i n t o d i s c r e t e c a t e g o r i e s based on processes employed. The range o f c o n t r o l and treatment technology used by o r i n d i c a t e d f o r each category was e v a l u a t e d t o determine what c o n s t i t u t e d best p r a c t i c a b l e " and "best a v a i l a b l e " technology. A summary o f t h e c u r r e n t discharge l i m i t a t i o n s f o r v a r i o u s f a c e t s o f t h e t i m b e r products i n d u s t r y i s g i v e n i n Table I . As shown i n t h i s t a b l e , a z e r o discharge o f process wastewater p o l l u t a n t s i s r e q u i r e d by EPA f o r a l l f a c e t s o f t h e t i m b e r products i n d u s t r y except wet storage o f l o g s , wet-process f i b e r products manufacture, and one segment o f the wood p r e s e r v i n g i n d u s t r y . T h i s requirement, by d e f i n i t i o n , h o l d s t h a t a z e r o discharge i s "the best p r a c t i c a b l e technology c u r r e n t l y a v a i l a b l e " by which t h e a f f e c t e d i n d u s t r i e s can c o n t r o l p o l l u t i o n . The technology i n d i c a t e d i n most cases i s i n - p l a n t process changes and m o d i f i c a t i o n s which w i l l permit r e c y c l i n g o f process water. S p e c i f i c e f f l u e n t l i m i t a t i o n s have been e s t a b l i s h e d f o r those segments o f t h e timber products i n d u s t r y f o r which a z e r o discharge was not judged t o be e c o n o m i c a l l y o r t e c h n i c a l l y f e a s i b l e . These l i m i t a t i o n s s e t f o r t h the average d a i l y discharge value f o r each p o l l u t a n t , based on 30 c o n s e c u t i v e days, as w e l l as t h e maximum one-day v a l u e . Expressed i n terms o f u n i t s o f p r o d u c t i o n , t h e l i m i t a t i o n s s e t maximum discharge v a l u e s f o r each p o i n t source o f p o l l u t i o n and, by s u b t r a c t i o n , i n d i c a t e the amount o f each p o l l u t a n t t h a t must be removed from process wastewater b e f o r e i t can be discharged. T y p i c a l e f f l u e n t l i m i t a t i o n s are shown i n Table I I f o r wood p r e s e r v i n g , h y d r a u l i c debarking, and steaming o f veneer l o g s .
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ff
Technology f o r Zero Discharge The exact technology used t o meet the e f f l u e n t l i m i t a t i o n s f o r an i n d u s t r y i s l e f t t o the i n i t i a t i v e o f the i n d i v i d u a l companies. However, the development document on which the e f f l u e n t l i m i t a t i o n s are based i n c l u d e s treatment and c o n t r o l technology. P l a n t s t h a t must meet a z e r o discharge requirement are more l i m i t e d i n t h e i r c h o i c e o f abatement measures than those t h a t are p e r m i t t e d a d i s c h a r g e , however s m a l l . Where the volnne i s l a r g e and discharge t o p u b l i c l y owned treatment works i s not p o s s i b l e , r e c y c l i n g i s the o n l y e c o n o m i c a l l y v i a b l e method o f a c h i e v i n g z e r o discharge. B a s i c a l l y , t h i s i n v o l v e s i n s t a l l i n g the equipment needed t o c l e a n up process water s u f f i c i e n t l y so t h a t i t can
Goldstein; Wood Technology: Chemical Aspects ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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Table I .
CHEMICAL
ASPECTS
Suranary o f d i s c h a r g e requirements f o r timber products industry
Industry Subcategory or Process
Discharge o f Process
Wet Storage o f Logs Log Washing Sawnills Particleboard I n s u l a t i o n Board Debarking Veneer M i l s (Hot-water v a t s ) (Steam chambers) Plywood M i l l s Finishing Wood P r e s e r v i n g (Steaming) (Boulton) (Salts) Hardboard (Dry p r o c e s s ) (Wet p r o c e s s ) Paper
Yes No No No Yes No
J
Water 1977 1983
Principal Pollutants
Yes No No No Yes No
Floating solids SS, BCD SS, BCD Phenols, BCD SS, BOD SS, BOD
No Yes No No
No No No No
BCD (phenols) BCD (phenols) BCD, Phenols BCD, Metals
Yes No No
Yes No No
Phenols, O i l s , CCD Phenols, O i l s , CCD Heavy M e t a l s , CCD
No Yes Yes
No Yes Yes
BCD, BCD, BCD,
c
b
SS SS SS
C o o l i n g water, y a r d r u n o f f , and b o i l e r blowdown are excluded from d e f i n i t i o n o f "process water." ^ E f f l u e n t g u i d e l i n e s l i m i t i n g t h e amount o f s p e c i f i c p o l l u t ants t h a t can be d i s c h a r g e d have been e s t a b l i s h e d f o r each process f o r which a d i s c h a r g e i s p e r m i t t e d . °Hydraulic debarking o p e r a t i o n s are p e r m i t t e d a d i s c h a r g e under 1977 g u i d e l i n e s , but not under 1983 g u i d e l i n e s .
Goldstein; Wood Technology: Chemical Aspects ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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Table I I . Surnnary o f e f f l u e n t standards f o r s e l e c t e d segments o f t h e wood p r o c e s s i n g i n d u s t r y
Industry Subcategory
Effluent Limitation 1983 1977 30-Day Dally Daily 30-Day Avg. Max. P o l l u t a n t Max. Avg. (kg/1000rn )
Wood P r e s e r v i n g Boulton P l a n t s Steaming P l a n t s
COD Phenol Oil & Grease pH
Salt Plants
No discharge o f p o l l u t a n t s p e r m i t t e d 110 550 220 1100 .064 .65 .21 2.18 3.4 12.0 6.9 6.0-9.0 No discharge o f p o l l u t a n t s p e r m i t t e d 24.0
3
(kg/m ) H y d r a u l i c Debarking Steam C o n d i t i o n i n g o f Veneer Logs
BCD TSS
1.5 6.9
0.5 2.3
BCD
0.72
.24
No discharge o f pollutants permitted
No d i s c h a r g e o f pollutants permitted
Goldstein; Wood Technology: Chemical Aspects ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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be reused i n the manufacturing process along w i t h i n i t i a t i n g s t r i c t water c o n s e r v a t i o n programs. Sources o f contaminated water i n t h e manufacture o f prod u c t s f o r which no wastewater discharge i s allowed i n c l u d e wettype debarking o p e r a t i o n s , steam o r hot-water c o n d i t i o n i n g o f l o g s , veneer d r i e r washwater, glue equipment washwater, and c e r t a i n t y p e s o f p r e s e r v a t i v e treatments. Only l i m i t e d d a t a are a v a i l a b l e on the q u a n t i t y and c h a r a c t e r i s t i c s o f these e f f l u e n t s (Table I I I ) . Each source o f wastewater i s d i s c u s s e d below i n terms o f t h e problem t h a t i t presents and the technology t h a t i s available to deal with i t . Debarking Operations. Debarking i s not o r d i n a r i l y a s i g n i f i c a n t source o f wastewater, except where h y d r a u l i c debarking i s employed. Where t h i s i s the case, water discharges i n the amount o f 50,000 t o 120,(XX) l i t e r s / M ^ o f wood are cannon. Since t h i s water has a BCD content i n the range o f 50 t o 250 m g / l i t e r , as w e l l as a r e l a t i v e l y h i g h content o f suspended s o l i d s , the e f f l u e n t from a h y d r a u l i c debarking o p e r a t i o n can be the most s i g n i f i c a n t p a r t o f the waste stream at p l a n t s employing t h i s technique. Because o f the l a r g e volume o f wastewater generated i n hy d r a u l i c debarking and t h e problems a s s o c i a t e d w i t h r e c y c l i n g i t , waste treatment and d i s p o s a l techniques used by the p u l p and paper i n d u s t r y are a p p l i c a b l e . T h i s i n v o l v e s t h e employment o f heavy-duty c l a r i f i e r s t o remove suspended s o l i d s , f o l l o w e d by b i o l o g i c a l treatment t o remove oxygen-demanding substances. H y d r a u l i c debarking i s being phased out by the i n d u s t r y — i n p a r t due t o the p o l l u t i o n problems a s s o c i a t e d w i t h i t s use and i n p a r t because o f the decrease i n the nuriber o f o v e r - s i z e d l o g s f o r which the technique was o r i g i n a l l y developed. Because o t h e r wet-type debarking methods generate r e l a t i v e l y l i t t l e wastewater, a l l o f which can be r e c y c l e d , i t i s not a n t i c i p a t e d t h a t debarking w i l l c o n t r i b u t e s i g n i f i c a n t l y t o the waste l o a d from p l a n t s i n the f u t u r e . Log C o n d i t i o n i n g . Veneer and plywood p l a n t s i n t h e U n i t e d S t a t e s use e i t h e r steam v a t s o r hot water v a t s t o c o n d i t i o n l o g s p r e p a r a t o r y t o p e e l i n g o r s l i c i n g . Steam v a t s are the more com mon n a t i o n a l l y , but both t y p e s are employed e x t e n s i v e l y i n the South and Southeast. Condensate from steam v a t s i s t h e major source of wastewater at p l a n t s t h a t use t h i s method o f c o n d i t i o n i n g . The volume v a r i e s w i t h the nuntoer and s i z e o f v a t s but amounts t o an estimated 114 l i t e r s / m i n u t e at p l a n t s w i t h annual p r o d u c t i o n s o f 9.31 m i l l i o n ΐβ. E f f l u e n t from t h e v a t s o f a t y p i c a l softwood plywood m i l l has a BCD l o a d i n g o f 410 kg/day at 2500 m g / l i t e r concentra t i o n and a t o t a l s o l i d s l o a d i n g o f 325 kg/day at 2,000 m g / l i t e r c o n c e n t r a t i o n . U n l i k e wastewater from other sources, t h a t from steam v a t s i s d i f f i c u l t t o e l i m i n a t e because t h e contaminated
Goldstein; Wood Technology: Chemical Aspects ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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Table I I I .
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Volume and c h a r a c t e r i s t i c s o f wastewater from s e l e c t e d wood products manufacturing o p e r a t i o n s f o r which no d i s c h a r g e o f p o l l u t a n t s i s p e r m i t t e d
Source of Wastewater
GOD
b c Suspended T o t a l Heavy Volume Solids S o l i d s Metals mg/1 (1/wk. )
Phenols
_ Debarking Log C o n d i t i o n i n g Steam v a t 4,900 0.44 Water v a t 7,293
