Page 311 - Industrial Wastewater Treatment, Recycling and Reuse

Urban Wastewater Treatment 285

Table 7.1 Typical characteristics of sewage wastewater in india
pH 5.5–8
Total solids 0.1%
TSS 100–700 mg/L
TDS 200–900 mg/L
BOD 100–400 mg/L
COD 200–700 mg/L
Nitrogen content 20–90 mg/L
Phosphorus content 5–20 mg/L
Chlorides 30–90 mg/L

an appreciable period of the year, barring the summer period when temper-

atures soar close to 40 C or even higher. The temperature is an important
parameter. Most municipal wastewaters are biologically treated using the
conventional aerobic process-activated sludge process (ASP). Temperature
here plays crucial role in the treatment because biological activity is strongly
temperature dependent, thereby directly affecting the efficiency of the bio-
logical processes. The lower the temperature, the lower the efficiency of the
biodegradation, thereby adversely affecting the process. The organics pre-
sent in the wastewaters need to be decomposed suitably and constitute
the major load on the biological treatment process. Typically, the organics
in the sewage wastewaters are biodegradable and do not require chemical
oxidation for making water suitable for discharge. The inorganic fraction,
particularly chlorides/salts, can be a major problem if the water is to be fur-
ther used for farming/irrigation because the salt presence can adversely affect
the land/soil quality and fertility. There are some phosphorus compounds
present in wastewaters that normally come from the use of soaps and deter-
gents apart from food residues. The nitrogen content in the wastewaters is
mainly in the form of proteins and amino acids. Both nitrogen and phospho-
rus are useful nutrients for the bacteria present in the biological processes.
However, salts of these two elements need monitoring, especially if the
water is to be reused.
The chemical oxygen demand (COD) for sewage wastewaters is not very
high, generally of the order of 200–700 mg/L. This is in stark contrast to
industrial wastewaters where typically the COD values range from 2000
to 4000 mg/L for textile wastewaters; 30,000 to 40,000 mg/L for dye
wasters, and as high as 150,000 to 200,000 mg/L for distillery wastewaters.
The biological oxygen demand (BOD) for sewage wastewaters is typically
below 400 mg/L. Further, the ratio of COD to BOD is generally of the
order of 1.7, although some variation is found depending on the nature