≪ ≫

Design of the CETPs

Table of Contents:

All the CETPs in the city have been designed to treat effluents to meet standards related to pH, suspended solids (SS), oil and grease, chemical oxygen demand (COD) and bio-chemical oxygen demand (BOD), but they have not been designed to meet the standards related to total dissolved solids (TDS) and heavy metals. The solution devised by the government and the industries for the TDS and heavy metals is to have an in-house treatment facility by member units, prior to sending the effluents to the CETPs. The treated effluents from the CETPs joins the treated sewage from the Pirana STP before being discharged into the Sabarmati. The treated industrial effluents from the mega pipeline mix with the treated sewage, resulting in the dilution of the treated effluents.

All the CETPs discussed for Ahmedabad are designed for physico-chemical treatment as primary treatment and biological treatment (with the help of bacteria) as secondary treatment. This type of design leads to an 85 per cent reduction in the pollution load. The design of all the CETPs is similar, irrespective of the fact that the member units are from varied sectors (chemical, pharmaceutical, dye-intermediates, textile, etc.) and that the CETP treats homogenous or heterogenous effluents. Since the treatment utilises the help of bacteria, the BOD becomes the main parameter to comment on the effectiveness of the CETPs in treating the pollution load. The COD, another important indicator of water pollution, has also been analysed.

A point worth noting is that the regulator does not prescribe the abatement method to treat the effluent—the polluter is allowed to choose it. The regulator only prescribes the standards for the treated effluent in its final form, ready to be discharged.

Standards prescribed to the CETPs

The CETPs have been prescribed ‘inlet’ standards for industrial effluents to be treated and the ‘outlet’ standards for the treated effluents from the CETP in the consent order (permit) issued by the GPCB. The industries are required to do in-house treatment to meet the CETP inlet norms. The inlet and outlet norms for the CETPs in Ahmedabad are presented in Table 8.3.

The inlet norms for the CETPs vary with respect to the BOD and the COD. For the BOD, the inlet norms vary from 300 mg/1 to 1200 mg/1, but the outlet norms are kept the same (30 mg/1) whereas for the COD, the range of the inlet norms is 1000 mg/1 to 3000 mg/1 but the outlet norm is again the same (250 mg/1) for all the CETPs. For CETP GVMM, inlet norms for the BOD and the COD are not specified by the regulator.

TABLE 8.3 Inlet and outlet standards prescribed to the CETPs in Ahmedabad

6.5-8.8

6.5-8.8

1200

30

3000

250

CETP Naroda

6.5-8.8

6.5-8.8

1200

30

3000

250

CETP OEPL

6.5-8.8

6.5-8.8

1200

30

3000

250

CETP OGEPA

6.5-8.8

6.5-8.8

300

30

1000

250

CETP GVMM

6.5-8.8

6.5-8.8

—

30

-

250

CETP Narol

6.5-8.8

6.5-8.8

700

30

2000

250

How effective are the CETPs in treating pollution?

The continuing levels of high pollution in the Sabarmati, even after the establishment of the environmental infrastructure to treat industrial effluents and domestic sewage, puts a question mark over the effectiveness of its performance. Of all the parameters for which the Sabarmati river quality has been analysed, as per ‘bathing water quality standards,’ TOOL is not included in the CETPs. The reason for this is that the CETPs treat only industrial effluents, while TCOL is attributed to sewage, which is treated separately in the STPs. COD, an important parameter for industrial effluents has been included in the analysis. Though the CETPs are not designed for treating heavy metals and the individual member units are supposed to treat them before sending the effluents to the CETP, the analysis is extended to include heavy metals in the treated effluents. The purpose is to examine whether there is a relationship between the presence of heavy metals in the CETP discharge and their presence in the river.

All the CETPs are seen to meet the standards for pH, at the inlet of the CETP as well as the outlet. Therefore, this parameter is not included in the detailed analysis for individual CETPs in the following paragraphs.

 
Source
Previous chapter
CETPs in Ahmedabad
Next chapter
CETP Vatva