What a Wastewater Limit Values Chart Actually Shows
A wastewater limit values chart is a regulatory table that lists, parameter by parameter, the maximum or minimum concentration allowed in an effluent stream before it can be discharged to a watercourse, sewer, irrigation area, or reuse application. Each row names a parameter (pH, suspended solids, COD, ammonia, fecal coliforms, etc.), the unit of measurement (mg/L, mS/m, count per 100 mL), and the numeric ceiling or floor the operator must meet at the sampling point. The chart is a compliance tool, not a treatment recipe: it tells the operator what the effluent must look like, not which unit operation produces it.
Standard parameters in the South African General Authorisation under the National Water Act 36 of 1998 include pH, electrical conductivity (mS/m), suspended solids (mg/L), chemical oxygen demand (mg/L), free chlorine (mg/L), fluoride (mg/L), soap/oil/grease (mg/L), ammonia as nitrogen (mg/L), nitrate/nitrite as nitrogen (mg/L), ortho-phosphate as phosphorus (mg/L) and fecal coliforms (count per 100 mL). The same document also lists sodium adsorption ratio (SAR) for the lower-volume irrigation tiers. Academic control-chart work on industrial wastewater, such as the multivariate Hotelling T² study published in the AIP Conference Proceedings (2017), confirms that BOD, COD and TSS are the parameters most often treated as standard in process-industry monitoring, with other analytes added depending on the discharge pathway.
Irrigation Limit Values by Daily Volume (Reference Tables)
The General Authorisation issued under the National Water Act 36 of 1998 publishes three numeric tables, one for each permitted irrigation volume. The text reproduced below is taken from the Centre for Environmental Rights revision of the General Authorisations (2013), which is the most widely cited consolidated version of the limits. All three tables apply to domestic wastewater or biodegradable industrial wastewater; non-biodegradable streams are excluded from the General Authorisation and require a formal water-use licence.
| Parameter | Limit (≤ 2,000 m³/day) |
|---|---|
| pH | 5.5–9.5 pH units |
| Electrical conductivity | Not more than 70 mS/m above intake, maximum 150 mS/m |
| Suspended solids | 25 mg/L |
| Free chlorine | 0.25 mg/L |
| Fluoride | 1 mg/L |
| Soap, oil and grease | 2.5 mg/L |
| Chemical oxygen demand (COD) | 75 mg/L |
| Faecal coliforms | 1,000 per 100 mL |
| Ammonia (ionised + un-ionised) as N | 3 mg/L |
| Nitrate/Nitrite as N | 15 mg/L |
| Ortho-phosphate as P | 10 mg/L |
| Parameter | Limit (≤ 500 m³/day) | Limit (≤ 50 m³/day) |
|---|---|---|
| pH | 6.0–9.0 pH units | 6.0–9.0 pH units |
| Electrical conductivity | 200 mS/m | 200 mS/m |
| COD | 400 mg/L (after removal of algae) | 5,000 mg/L (after removal of algae) |
| Faecal coliforms | 100,000 per 100 mL | 100,000 per 100 mL |
| Sodium adsorption ratio (SAR) | ≤ 5 for biodegradable industrial wastewater | ≤ 5 for biodegradable industrial wastewater |
The General Authorisation defines "biodegradable industrial wastewater" as wastewater containing predominantly organic waste from milk processing, fruit and vegetable manufacture, sugar mills, soft-drink bottling, breweries and wineries, animal feed manufacture, gelatine and glue from hides, abattoirs, fish processing, and confined animal feeding operations. Location rules apply to all three tiers: irrigation must take place at least 50 m above the 1-in-100-year flood line, at least 100 m from any watercourse, and outside a 500 m radius of any wetland or borehole used for drinking water or stock watering.
Discharge Limits vs. Irrigation Limits: Why the Numbers Differ
The General Authorisation treats disposal into a water resource as a separate water-use activity from irrigation, with its own Table 2.1 "Wastewater limit values applicable to discharge of wastewater into a water resource" published in the same notice. The irrigation tables assume the soil and crop act as a polishing step; a direct pipe or canal discharge to a river, dam or wetland does not have that buffer, so the limits in Table 2.1 are generally tighter than the high-volume irrigation tier, and the receiving environment is not used as a treatment unit. Operators must consult Table 2.1 separately because the General Authorisation document does not reproduce it alongside Tables 1.1–1.3.
Monitoring obligations differ by activity. Under the General Authorisation, irrigation quantity must be metered and the total recorded weekly, and quality must be monitored by a monthly grab sample taken at the point where the wastewater enters the irrigation system, for every parameter listed in the relevant tier. The discharge pathway has its own volume and quality record-keeping rules, and the responsible authority may require additional sampling points. A facility that mixes biodegradable industrial wastewater with non-biodegradable streams — metal finishing rinse water, chemical plant effluent, refinery process water — is typically excluded from the General Authorisation and must apply for a water-use licence, which carries bespoke numeric limits negotiated with the regulator rather than the chart values reproduced above.
Matching Each Parameter to the Unit Operation That Hits It
The compliance chart becomes useful for procurement only when each line item is paired with the unit operation that reliably moves that parameter. The mapping below is built from the General Authorisation's parameter list (CER, 2013) and from the parameter-by-parameter process discussion in the pharmaceutical wastewater review by Periodica Polytechnica Chemical Engineering, which flags COD as the parameter most likely to exceed emission limits in fine-chemical effluents and the one driving technology choice in that sector.
| Parameter (tightest tier) | Primary unit operation | Function in the process train |
|---|---|---|
| pH (5.5–9.5 or 6.0–9.0) | PLC-controlled chemical dosing skid for pH correction | Acid or caustic dosing upstream of equalization |
| Suspended solids (≤ 25 mg/L); soap/oil/grease (≤ 2.5 mg/L) | Dissolved air flotation (DAF) system for suspended solids and oil/grease removal | Primary clarification, FOG and colloidal removal |
| COD (≤ 75 mg/L tightest; up to 5,000 mg/L at 50 m³/day) | MBR membrane bioreactor for COD, BOD and ammonia-nitrogen removal | Biological oxidation; membrane retains biomass |
| Ammonia-N (≤ 3 mg/L); nitrate/nitrite-N (≤ 15 mg/L); ortho-phosphate-P (≤ 10 mg/L) | MBR membrane bioreactor for COD, BOD and ammonia-nitrogen removal | Nitrification/denitrification and bio-P or chemical P precipitation |
| Faecal coliforms (≤ 1,000/100 mL tightest; ≤ 100,000/100 mL lower tiers) | UV sterilizer for fecal coliform and pathogen reduction | Disinfection at the irrigation or discharge point |
| Electrical conductivity (≤ 150 mS/m tightest; ≤ 200 mS/m otherwise) | Reverse osmosis or strong ion exchange | Dissolved-salt removal; DAF, biological and disinfection steps have negligible effect on EC |
| Free chlorine (≤ 0.25 mg/L); fluoride (≤ 1 mg/L) | Dechlorination (sulphite dosing) and fluoride-specific adsorption or RO | Polishing step before irrigation main |
For sites that discharge to a sewer rather than a watercourse, the same unit operations apply but the limits are set by the local pretreatment ordinance. The chemical-plant pretreatment compliance guide and the mining and metals wastewater pretreatment guide walk through the same parameter-to-technology mapping against US-style pretreatment limits, which is useful for any reader comparing the South African irrigation framework against a sewer permit.
A 2026 Decision Framework: From Chart Value to Equipment Sizing
Translating a chart value into a purchase order is a five-step exercise. Step 1: identify which General Authorisation tier (or water-use licence schedule) applies to the site's daily wastewater volume and disposal pathway — this fixes the limit values to design against. Step 2: characterise the influent for the same parameters at the same units; where the influent value is unknown, request a 24-hour composite sampling programme before sizing. Step 3: map each parameter that exceeds the limit to the unit operation in the table above and build the process train in order — mechanical bar screening first, then equalization and PLC-controlled chemical dosing skid for pH correction, then DAF, then biological treatment in an MBR membrane bioreactor for COD, BOD and ammonia-nitrogen removal (or a packaged integrated sewage treatment plant for smaller flows), then UV, then RO only where the conductivity limit demands it. Step 4: confirm monitoring obligations — weekly volume metering, monthly grab sampling at the discharge or irrigation point, and a written record-keeping system as required by the General Authorisation and standard for most 2026 pretreatment permits. Step 5: where the influent parameter list includes AOX, heavy metals, or COD with refractory organics typical of pharmaceutical and fine-chemical streams, expect a tighter, licence-driven limit set and budget for distillation or membrane polishing, with sludge dewatering sized to the biological wasted mass and a multi-media filter for any reuse polishing step.
Frequently Asked Questions
How should a buyer read a wastewater limit values chart?
Read each row as a numeric ceiling (or floor, for pH) that the effluent must meet at the sampling point named in the regulation. Match the unit exactly — mg/L for chemical analytes, mS/m for electrical conductivity, count per 100 mL for fecal coliforms — and check the table scope before applying the value, because the irrigation tiers in the South African General Authorisation (CER, 2013) are tied to daily volume and to whether the wastewater is domestic or biodegradable industrial.
Which parameters drive wastewater equipment cost the most?
COD and ammonia are the parameters that drive the size and cost of the biological step, because they fix the reactor volume, aeration demand, and membrane area in an MBR. Conductivity, when the limit is below the influent value, forces a reverse-osmosis or ion-exchange polishing step that often costs more than the biological train itself; where the limit allows up to 200 mS/m, that cost is avoided. Sludge handling — typically a plate-and-frame filter press — must be sized off the biological wasted mass, not the influent COD, so the buyer should request a wasted-sludge calculation from each bidder rather than accept a percent-of-influent assumption.
