Process control · Chemical dosing

Effluent Neutralisation —
Food Production Site

Automatic acid dosing for a pH 12 production effluent — designed for a strong base, a strong acid and a flow that never stays the same.

Client Industrial food producer, Belgium

Partner Ecotechnic (ecotechnic.be)

Domain Process control · Chemical dosing · Effluent treatment

Status Delivered to the client — September 2026

Scope Process design · Control logic · Dosing line · Material selection

Context

An alkaline effluent that can't leave the site as it is

The site's production generates an effluent at around pH 12 — far outside what can be discharged. It has to be neutralised continuously, on site, before it leaves.

Neutralising a strong base with a strong acid sounds simple. In practice, it is one of the more demanding dosing problems: near neutrality, a few millilitres of acid move the pH by whole units, while at peak flow the acid demand is high.

The brief: an automatic dosing system that keeps the outlet within limits across the full operating range, with a dosing line able to handle concentrated sulphuric acid safely.

The hard part

A steep titration curve

Between a strong base and a strong acid, the pH curve is nearly vertical around neutrality. Too little acid and the outlet stays alkaline; slightly too much and it overshoots into acid. The control has to be both strong and fine.

A moving target

Effluent flow, temperature and alkalinity vary with production. A dose that is right one minute is wrong the next — the control has to follow the process, not a fixed setpoint.

Concentrated H₂SO₄

Concentrated sulphuric acid attacks a large share of common piping and fitting materials. Every component in contact with the reagent had to be checked for compatibility, not assumed.

Solution

One pump, fine control on two pH measurements

The dosing is driven by pH measured before and after the dosing point, with corrections for effluent temperature and flow. The pump output is driven by a 4–20 mA analogue signal, for a continuous range from fine trimming to full dose.

The initial design used two pumps in split range. In operation, a single pump with finer control proved the better answer — and the simpler one to maintain.

The control logic runs on a Siemens LOGO! controller — a deliberately simple, robust and locally maintainable platform for a process that has to run unattended.

The dosing line is built in PTFE and PVDF throughout, with CPVC (Corzan) used as a single, deliberate exception where it was the pragmatic choice.

Technical details

Process

Continuous neutralisation of a pH 12 alkaline effluent with sulphuric acid.

Measurement

pH before and after dosing (Hach). Ultrasonic flow measurement — Pulsar dB Mach 3 on an Ultra 4 controller. Effluent temperature.

Dosing

Single dosing pump (ProMinent). Output driven by 4–20 mA analogue signal.

Control

Siemens LOGO! controller. Fine control on both pH values, compensated for temperature and flow.

Materials

PTFE / PVDF dosing line. CPVC (Corzan) as a single justified exception.

Partner