Standards for Ambient Air, Noise Emission & Effluents - 1 | Environmental Engineering - Civil Engineering (CE) PDF Download

National Ambient Air Quality Standards

The notifications on National Ambient Air Quality Standards were published by the Central Pollution Control Board in the Gazette of India. The notifications were issued vide notification No(s). S.O. 384(E), dated 11^th April, 1994; S.O. 935(E), dated 14^th October, 1998; and S.O. 217 in Part III section 4, dated 18^th November, 2009.

The standards specify concentration limits for common air pollutants and define monitoring and compliance requirements. Typical pollutants covered under ambient air quality standards include particulate matter (PM10, PM2.5), sulphur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), ozone (O3), lead (Pb) and other toxic components such as benzene, arsenic, nickel and benzo(a)pyrene where applicable. Standards are expressed in mass concentration units (for example, µg/m³ for particulate matter and gaseous pollutants; mg/m³ or ppm for certain gases where appropriate) and in averaging periods (annual, 24-hour, 8-hour, 1-hour).

• Annual arithmetic mean: Minimum 104 measurements in a year at a particular site taken twice a week, each measurement being 24-hourly at uniform intervals.
• Short-term averages: 24-hourly or 08-hourly or 01-hourly monitored values, as applicable, shall be complied with 98% of the time in a year. For the remaining 2% of the time, monitored values may exceed the limits but not on two consecutive days of monitoring.

Note: Whenever and wherever monitoring results on two consecutive days of monitoring exceed the limits specified above for the respective category, it shall be considered adequate reason to institute regular or continuous monitoring and further investigation.

General Standards For Discharge of Environmental Pollutants

These standards are applicable to industries, operations or processes other than those for which specific standards have already been specified in the Schedule to the Environment (Protection) Rules, 1986/1989. They define maximum allowable concentrations or loads for various effluent parameters that may be discharged to inland surface waters, public sewers, marine waters, and on land.

Part - A: Effluents

Scope and common parameters: Part A generally lists parameter limits for direct discharge of treated wastewater (effluents) to different receiving media. Typical parameters and their significance are:

• pH - affects aquatic life and chemical reactions; limits prevent corrosive or strongly alkaline discharges.
• BOD (Biochemical Oxygen Demand) - indicates biodegradable organic matter; high BOD reduces dissolved oxygen in receiving water.
• COD (Chemical Oxygen Demand) - measures total oxidisable pollutants, including non-biodegradable organics.
• Total Suspended Solids (TSS) - affects light penetration and sedimentation in water bodies.
• Oil & grease - harmful to aquatic organisms and affects oxygen transfer.
• Temperature - thermal discharges can affect dissolved oxygen and biological communities.
• Heavy metals (for example Pb, Cd, Cr, Ni) - toxic and bioaccumulative; specific limits are provided.
• Residual chlorine - if used for disinfection; excess harms aquatic life.

Standards in Part A are typically presented as concentration limits (mg/L or µg/L) for various receiving environments and types of discharge. Industries must ensure effluent treatment systems reduce pollutants to meet these limits before discharge.

Part - B: Wastewater Generation Standards

Objective: Part B provides guidance on allowable wastewater characteristics at the point of generation for different categories of industries and processes. These standards are used to design in-plant treatment systems and segregation schemes so that final effluents meet Part A limits.

Key considerations:

• Segregation of streams (highly contaminated vs. low strength) to enable appropriate treatment and reuse.
• Reduction of pollutant concentrations at source through cleaner production, process modification and good housekeeping.
• Monitoring of flow and pollutant concentrations to quantify generation and assess compliance.

Part - C: Load Based Standards

Definition and rationale: Load based standards specify the total mass of a pollutant that may be discharged per unit time (for example, kg/day or kg/year) by a source or plant, rather than concentration alone. They are useful where discharge dilution varies, or where cumulative loading to a water body must be controlled.

Load calculation: The usual relation to convert concentration to load is:

Load (kg/day) = Concentration (mg/L) × Flow (m³/day) ÷ 1000

This permits regulators and designers to set limits on total pollutant mass and to assess the contribution of individual sources to the overall pollutant load of a receiving water body.

1. Petroleum Oil Refinery

For refineries, load based limits are commonly applied to parameters such as oil & grease, phenols, BOD, COD, sulfides and specific toxic compounds. Load based standards take into account refinery processing capacity and typical wastewater generation rates to establish allowable pollutant mass emissions.

2. Large Pulp & Paper, News Print/Rayon grade plants of capacity above 24,000 tonne/annum

For large pulp and paper plants, load based standards address parameters including BOD, COD, TSS, colour, chlorinated organic compounds, and solids associated with pulping and bleaching operations. Standards reflect the high volumes and characteristic contaminants from these processes and are scaled with plant capacity.

Monitoring, Compliance And Enforcement - Key Points

Monitoring frequency and protocol:

• Ambient air monitoring must follow standard sampling methods and approved instruments; averaging periods and required % compliance are provided in the standards (for example the 98% rule for certain short-term averages).
• Effluent sampling must be representative of the discharge-grab samples for instantaneous parameters and composite samples for parameters representing average load over a period.
• Continuous monitoring (online analysers) may be required where two consecutive days of monitoring exceed limits or for high-risk industries to provide real-time data to authorities.

Compliance assessment: Compliance is assessed by comparing monitored values against the relevant standard for the parameter, averaging period, and location (ambient monitoring site, point of discharge, receiving water). In addition to concentration limits, load based and generation standards are used to assess total environmental impact.

Actions on non-compliance: Two consecutive days of exceedance in monitored results are considered sufficient reason to institute regular or continuous monitoring and further investigation. Regulatory actions can include notice for corrective measures, directions for improved treatment, penalties, or shutdown until compliant operation is demonstrated.

Noise Emission - Principles And Practical Considerations

Overview: Noise emission standards set permissible sound pressure levels for different zones (for example residential, commercial, industrial, and silence zones). They specify measurement metrics (most commonly A-weighted sound levels, dB(A)) and may define limits for day and night time periods.

Measurement and indicators:

• Leq (equivalent continuous A-weighted sound level) is the commonly used metric for assessing environmental noise over a given time period.
• Measurements are taken using calibrated sound level meters following national or international standards; long-term monitoring may use logging instruments to record time histories.
• Noise mapping and planning are used in urban areas to identify hotspots and plan mitigation (barriers, building insulation, traffic management).

Control measures: Engineering controls at the source, administrative controls (time restrictions for noisy activities), zoning, and providing quiet building designs are the usual mitigation approaches. For industrial facilities, equipment enclosures, acoustic lagging and maintenance reduce emission.

Summary

The national standards for ambient air, noise emission and effluents provide the regulatory framework to protect public health and the environment. They specify pollutant-wise concentration limits, averaging periods and monitoring protocols, include special provisions such as the 98% compliance rule for short-term averages and the requirement for increased monitoring when exceedances occur on two consecutive days, and cover concentration-based, generation-based and load-based requirements. Civil engineers and environmental professionals must apply these standards when designing treatment systems, planning land use, preparing environmental impact assessments and implementing pollution control measures.