Appendix I-C 
Chemical and Biological Processes 
A comparison was made of waste stream pollution 
for cliemical and biological processes. Ideally, the 
comparison should he between the two processes 
used in the production of the same end product. 
Since such data do not currently exist at the in- 
dustrial level, the comparison was made between the 
chemical production of a mixture of chemicals and 
the biological production of alcohol and antibiotics. 
One noteworthy parameter is the 5-day biochemical 
oxygen demand (BODS) —the oxygen required over a 
5-day period by organisms that consume degradable 
organics in the waste stream. If the oxygen demand 
is too high, the discharge of such a stream into a 
body of water will deplete the dissolved oxygen to 
the point that it threatens aquatic life. An important 
variable that must be considered along with the BOD 
is the COD (the chemical oxygen demand). Large dif- 
ferences between the COD and BOD of a waste sys- 
tem can indicate the presence of nonhiodegradahle 
substances. Although the conventional process 
stream shown in table I-C-1 has less BOD5 than the 
biological process stream, its COD content probably 
means that nonbiodegradables are present, and 
specialized waste treatment is necessary. 
BOD is one area where traditional fermentation 
based processes have posed pollution problems. 
Batch fermentation processes typically generate 
large quantities of dead cells and residual nutrients 
that cause a large BOD if they are dumped directly 
into a dynamic aquatic environment. (See table I-C-1.) 
This difficulty can be circumvented by the use of 
spent cell material as an animal feed supplement or 
Table I-C-1.— Waste Stream Pollution Parameters: 
Current Processes v. Biological Processes 
Compounds: IVlixed chemicals, including ethylene 
oxide, propylene oxide, glycols, amines, and ethers 
Pollution parameters 
Current 
processes 
Biological 
processes 
Alkalinity (mg/I) 
4,060 
0 
BOD53(mg/l) 
1,950 
4,000-12,000 
Chlorides (mg/I) 
430-800 
0 
CODb(mg/l) 
7,970-8540 
5,000-13,000 
Oils (mg/I) 
547 
0 
pH 
9.4-9.8 
4-7 
Sulfates (mg/I) 
655 
0 
Total nitrogen (mg/I) 
1,160-1,253 
50-200 
Phosphates (mg/I) 
0 
50-200 
®5-day biological oxygen demand. 
*^Chemical oxygen demand. 
SOURCE: Office of Technology Assessment. 
as a fertilizer. These a|)|)lications ha\(> Imumi inten- 
sively in\ estigated and ha\ (t met u ilh success. 
Because of the renewed inlc'resl gnK'ralefl hy the 
potentials of genetic ('iigineering, souk* traditional 
fermentation .systems ar«f Ix'ing reih'signed. Immo- 
hilization allows the rmise of c(*lls that would other- 
wise he discarded. These .systems c;m he used con- 
tinuously for se\eral months as compared with the 
usual fermentation tim(> in a hatch process of about 
one week or less. Immohilizc'd operations create 
waste cells much U'ss often than h;itch s\stems. .md 
therefore generate less BOI ). 
292 
