EMS model
3.2.2 Monitoring of emissions to water
3.2.2.1 Monitoring of influent and effluent waste waters of a WWTP Description Description
Proper operation of a WWTP requires the monitoring and targeted adjustment of various process parameters in the influent and effluent of the WWTP. Monitoring of the relevant parameters can be accomplished by online measurements (that facilitate rapid intervention and control) or analytical results derived from waste water samples [ 251, Ullmann's 2000 ].
Parameters to be monitored and the frequency of monitoring depend on the characteristics of the waste water to be treated, the final effluent discharge medium and the waste water treatment techniques used within the WWTP.
Important parameters are also monitored at the level of each waste water treatment technique comprising the WWTP to ensure the proper operation of the techniques and the subsequent treatment steps. This specific monitoring is not described in this section but is generally addressed, if relevant, in the sections dealing with individual treatment techniques (see Section 3.3.2.3).
Table 3.3 summarises the information collected from the questionnaires on parameters monitored in the influent and effluent of the WWTPs. The data collection was restricted to a set of common parameters and did not include, for example, the common chromatographic detection of site-specific organic compounds. When data on influent or effluent concentrations were provided, these data were usually accompanied with some information on the monitoring.
For example, TSS values in the effluent were reported by 76 out of 95 directly discharging WWTPs, and for 65 (or 86 %) of these some information on the monitoring was provided.
However, this information was often incomplete (e.g. on frequency, sampling regime, or analytical method used).
The parameters monitored have been grouped into two categories: routinely monitored parameters and non-routinely monitored parameters. Routinely monitored parameters are the ones for which data were reported in more than 50 % of the 95 questionnaires analysed. Non-routinely monitored parameters are the ones for which data were reported in less than 50 % of the 95 questionnaires analysed. The monitoring frequencies of the parameters have also been extracted from the questionnaires as provided in Table 3.3. However, the measurement frequency was not reported in all questionnaires. The monitoring frequency of any parameter depends on many factors such as the origin of the waste water and type of contamination (e.g. if the influent waste water contains high AOX levels, then the frequency of AOX measurements might be higher), the influent load of contaminants (e.g. high concentrations of heavy metals), type of recipient water body (whether it is a creek or a sea will affect the frequency of monitoring of a certain parameter), the effluent waste water flow rate compared to the flow rate of the water body and the monitoring requirements set by the Member States (see also the Reference Report on Monitoring of Emissions to Air and Water from IED installations (ROM) [ 101, COM 2016 ]).
Regarding the monitoring of emissions, they shall be carried out in accordance with EN standards or, if EN standards are not available, ISO, national or other international standards which ensure the provision of data of an equivalent scientific quality.
Table 3.3: Monitoring regimes reported for the WWTPs
Parameter Frequency
Influent to the WWTP
Routinely monitored Waste water flow Continuous
pH Continuous Temperature Continuous
COD Continuous Daily/weekly/monthly Non-routinely monitored
TOC Continuous Daily/weekly/monthly BOD5 Daily/weekly/monthly Total suspended solids (TSS) Daily or other
Total nitrogen (TN) (1) Continuous Daily/weekly/monthly Total inorganic nitrogen (Ninorg) (1) Daily/weekly or other
Ammonia (NH4-N) Daily/weekly or other Nitrite (NO2-N) Daily/weekly or other Nitrate (NO3-N) Daily/weekly or other Total phosphorus (TP) Continuous Daily/weekly/monthly or other Orthophosphate (PO4-P) (2) Daily/weekly
AOX Daily/weekly/monthly Heavy metals (3) Daily/weekly/monthly or other Bacteria toxicity (2) Daily/monthly
Phenols (2) Daily/weekly or other Chloride (2) Daily/weekly or other Sulphate (2) Daily/weekly/monthly Cyanide(free) (2) No information provided
Other (4) Site-specific
Effluent from the WWTP
Routinely monitored Waste water flow Continuous
pH Continuous Daily or other Temperature Continuous
COD Daily/weekly/monthly or other BOD5 Daily/weekly/monthly or other Total suspended solids (TSS) Continuous Daily/weekly/monthly or other
Total nitrogen (TN) (1) Daily/weekly or other Total inorganic nitrogen (Ninorg) (1) Daily/weekly or other
Ammonia (NH4-N) Daily/weekly or other Nitrite (NO2-N) Daily/weekly or other Nitrate (NO3-N) Daily/weekly or other Total phosphorus (TP) Daily/weekly/monthly or other Orthophosphate (PO4-P) (2) Daily/weekly
Heavy metals (3) Daily/weekly/monthly or other Chloride (2) Daily/weekly/monthly or other Non-routinely monitored
TOC Daily or other
AOX (2) Daily/weekly/monthly or other Toxicity (e.g. fish or fish egg, daphnia, algae,
luminescence) (2) Monthly or other
Sulphate (2) Daily/weekly/monthly or other Phenols (2) Daily/weekly/monthly or other Cyanide (free) (2) Monthly or other
Other (hydrocarbons, fluoride, etc.) (4) Site-specific (1) Refers only to biological WWTPs.
(2) Corresponding data were only collected during the first survey.
(3) The following heavy metals were asked for in both surveys: Cd, Cr, Cu, Hg, Ni, Pb, Zn. The heavy metals monitored are site-specific based on the characteristics of the waste water to be treated and the final effluent discharge medium.
(4) Other parameters (e.g. hydrocarbons, fluoride) can be included in the monitoring regime depending on the characteristics of the waste water to be treated, the type of treatment techniques used and the final effluent discharge medium.
Source: [ 222, CWW TWG 2013 ].
Achieved environmental benefits
Monitoring of influent and effluent waste water of a WWTP helps to maintain the proper operation of the WWTP and to detect accidental releases and thus helps to prevent any possible adverse environmental effects upon discharge of waste waters.
Cross-media effects
Some equipment, chemicals and energy are required for carrying out monitoring. The COD measurement relies on the use of very toxic compounds (i.e. mercury and chromate).
Operational data
The parameters to be monitored in the influent to, and effluent from, the WWTP and the frequencies of monitoring depend on the characteristics of the waste water, the final effluent discharge medium and the type of treatment techniques used.
Table 3.4 gives the monitoring regime of a WWTP from Germany (WWTP #06).
Table 3.4: Monitoring regime of an example WWTP
Parameter Influent Effluent
Waste water flow Continuous Continuous
pH Continuous Continuous
Temperature Continuous Continuous
TOC Monthly mixed sample 24-h mixed sample, daily
BOD5 24-h mixed sample, weekly 24-h mixed sample,
weekly
COD Monthly mixed sample Monthly mixed sample
TSS NM Continuous, as turbidity
AOX Monthly mixed sample 24-h mixed sample,
weekly + monthly mixed sample
Total chromium Monthly mixed sample Monthly mixed sample
Total copper Monthly mixed sample 24-h mixed sample,
weekly + monthly mixed sample
TN (as N) Monthly mixed sample Total inorganic N
Ammonia (NH4-N) NM 24-h mixed sample, daily
Nitrite (NO2-N) NM 24-h mixed sample, daily
Nitrate (NO3-N) NM 24-h mixed sample, daily
TP Monthly mixed sample 24-h mixed sample,
weekly + monthly mixed sample
Chloride NM 24-h mixed sample, daily
Sulphate NM 24-h mixed sample, daily
+ monthly mixed sample NB: NM = not monitored.
Source: [ 222, CWW TWG 2013 ].
The monitoring regime given in Table 3.4 is specific to the WWTP in question and cannot be generalised to other WWTPs.
Applicability
Generally applicable to all WWTPs.
Economics
Driving force for implementation
To ensure the proper operation of the WWTP and to ensure that the required quality of the effluent waste water from the WWTP is met and in line with the effluent discharge criteria are the driving forces for the implementation of this technique.
Example plants
All WWTPs have a specific monitoring regime depending on the raw waste water characteristics, treatment techniques used and the final effluent discharge medium [ 222, CWW TWG 2013 ].
Reference literature
[ 101, COM 2016 ] [ 222, CWW TWG 2013 ] [ 251, Ullmann's 2000 ]
3.2.2.2 Toxicity tests