Tannery And Leather Industry Solutions In Pakistan

Tannery effluent treatment in Pakistan needs chemistry and measurement from the same supplier, and Khan Associates provides both from its Lahore and Karachi offices: coagulants, flocculants and decolouring agents for the ETP, laboratory instruments for chromium, sulphide, COD and BOD, and online analysers and flow meters for the plant itself.

Chromium control is one of the applications where that combination matters most. It depends on holding a narrow pH endpoint at chrome precipitation and on producing a total or hexavalent chromium result that a regulator or a brand auditor will accept. Every chemistry recommendation starts with a jar test on your own effluent: send us your effluent analysis and we will come back with a tested recommendation and a quotation.

Why The Streams Have To Be Kept Apart

If acidic tanyard liquor meets alkaline sulphide-bearing beamhouse liquor, the sulphide is liberated as hydrogen sulphide gas. This is not a theoretical concern. It is the single most common reason for odour complaints, worker safety incidents and inspector attention at Pakistani tanneries, and it usually traces back to a drainage layout that was never designed for segregation, or to a sulphide oxidation step that has stopped performing.

Stream segregation is therefore the first thing to establish before discussing chemistry at all. Beamhouse liquor should reach catalytic sulphide oxidation before it mixes with anything acidic. Chrome float should reach precipitation or recovery separately. Only after those two streams have been dealt with does it make sense to equalise everything and start dosing coagulant.

Where a plant cannot physically segregate, sequencing has to be managed in time instead of in space, and that requires knowing the sulphide concentration in the beamhouse stream rather than guessing at it. It is the point at which the treatment discussion and the analytical discussion stop being separate conversations.

Chrome Liquor: Precipitation, Recovery And pH Control

Chromium precipitation is straightforward chemistry executed at a narrow pH endpoint. Raise the pH of the segregated chrome float with an alkali and chromium comes out as the hydroxide, which can either be dewatered and disposed of or redissolved in sulphuric acid and returned to the tanyard. Miss the endpoint and residual chromium stays in solution, passes downstream, and ends up either in your discharge sample or adsorbed onto sludge you now have to handle as chrome-bearing waste.

The failure here is almost never the chemistry. It is control. Manual pH checks on a batch that is still reacting will not hold an endpoint reliably, which is why plants running chrome precipitation at any scale move to instrumented pH measurement, either with portable meters used to a disciplined schedule or with a permanently installed sensor on a digital controller. We supply HACH instruments and reagents for both, including HQ series portable meters with IntelliCAL probes and the sc controller platform where measurement needs to be continuous. Verification is separate from control: residual chromium in the supernatant after precipitation is an analytical determination, not a process reading.

Sludge Dewatering And The Cost Of Disposal

Chrome-bearing sludge is expensive to dispose of, and every percentage point of cake dryness you fail to achieve is volume you are paying to move. Dewatering performance on a belt press, decanter or centrifuge depends on matching polymer charge density and molecular weight to the sludge, which for tannery sludge means a high-charge cationic grade in most cases. Getting this wrong shows up as poor cake release, low solids capture and polymer consumption that keeps climbing.

We supply Japanese MT AquaPolymer flocculant grades, covering the ARONFLOC powder series and the ACCOFLOC emulsion series across nonionic, anionic and cationic types, with over a hundred grades available. As with coagulant selection, grade selection starts with a jar test on your own sludge.

The Tannery ETP Laboratory: The Numbers You Have To Report

Under the National Environmental Quality Standards for municipal and liquid industrial effluents, discharge to inland waters is limited on pH at 6 to 9, BOD at 80 mg/l, COD at 150 mg/l, TSS at 150 mg/l, TDS at 3,500 mg/l, sulphide at 1.0 mg/l, ammonia at 40 mg/l and oil and grease at 10 mg/l, with chromium in both its trivalent and hexavalent forms listed as a regulated parameter. Enforcement is provincial, which means Punjab EPD in Kasur, Lahore, Sialkot, Gujranwala and Multan, and Sindh EPA in Korangi.

That list translates into a fairly specific bench. A laboratory spectrophotometer with a digestion reactor and a reagent system covers COD, nitrogen and several metal and anion parameters, which is why HACH DR series instruments with TNTplus vial chemistry and a DRB200 reactor are the common backbone of an effluent laboratory. Alongside that, COD thermoreactors and respirometric BOD sensor systems from VELP COD and BOD systems handle high-throughput oxygen demand work, and VELP Kjeldahl digestion and distillation units cover total Kjeldahl nitrogen and ammoniacal nitrogen, which matter more at a tannery than at most other industrial plants because of the protein and deliming load.

The supporting equipment is not optional either. A BOD5 determination needs a temperature-controlled incubator. TSS needs a drying oven. Sample preparation needs water baths, stirrers and distilled water. Zenith Lab incubators and drying ovens cover this layer, while centrifuges, sterilizers and water distillers complete the ETP laboratory bench.

Chromium Analysis: Effluent, Sludge And Finished Leather

Chromium is one of the parameters that regulators and brand auditors look at most closely, and it has to be measured in three different places, each with its own method.

In effluent and sludge, what you usually need is total chromium, at levels where a photometric method may be adequate for routine control but atomic absorption spectrometry gives you the sensitivity and defensibility that a disputed result requires. Wayeal atomic absorption spectrophotometers cover that duty for a tannery laboratory.

In finished leather, the question is hexavalent chromium, and here the method is prescribed. ISO 17075-1 is the colorimetric route, extracting the leather under defined conditions and reading the developed colour on a spectrophotometer. ISO 17075-2 is the ion chromatography route, and where both are applied the ion chromatography result is treated as the reference, because it avoids the interference that coloured extracts cause in the colorimetric method. Both quantify down to 3 mg/kg, and sample preparation follows ISO 4044. Hexavalent chromium can also form after production during storage and ageing, which is why brands test finished articles rather than accepting process control as proof.

For a Pakistani tannery exporting to brands with restricted substance requirements, that currently means sending samples abroad or to a small number of accredited laboratories and waiting. Building the capability in-house is a real option: the colorimetric method needs a spectrophotometer and controlled extraction, the reference method needs an ion chromatograph, and Wayeal analytical instruments cover both ion chromatography and AAS at a cost well below the comparable European and Japanese platforms. Chromic oxide content in leather, expressed as a percentage rather than in mg/kg, is a separate determination and again an AAS or titrimetric job depending on the method your buyer specifies.

What Is Worth Monitoring Online, And What Is Not

Online instrumentation earns its cost where a measurement drives a control action or where a regulator expects a continuous record. At a tannery ETP, that is a short list.

pH at chrome precipitation and at equalisation is worth instrumenting, because both are control points where a drift causes a downstream failure. Dissolved oxygen in the aeration basin is worth instrumenting, because it governs aeration energy and biomass health, and tannery biology is already under stress from sulphide and chromium carry-over. HACH sc controllers with digital probes cover both. Continuous COD, ammonia and TSS at the final outfall are worth considering where a provincial authority or a brand audit expects a continuous record rather than grab samples, and Wayeal online effluent analysers cover those parameters.

What we would not recommend is putting chromium online. Continuous chromium analysis on tannery effluent is a demanding application, the maintenance burden is real, and for most plants the money is better spent on reliable pH control at the precipitation stage plus disciplined laboratory verification.

Measuring Water In And Effluent Out

Flow measurement used to be an afterthought at a tannery. It is not any more. The Leather Working Group audit protocol assesses water and energy consumption per unit of leather produced, which means an unmetered intake is a scoring problem before it is an engineering one. The current protocol also distinguishes between direct discharge from an on-site effluent plant and indirect discharge to a central or municipal plant, so the volume leaving your site is a number you are expected to know.

Retrofitting a meter onto an existing line is usually the obstacle, since nobody wants to cut pipe and stop production. McCrometer’s FPI Mag insertion meter installs by hot tap on a live line without dewatering or cutting, which makes it a practical retrofit for an intake main or an outfall that was never designed with a meter in it. Full-bore Ultra Mag and Dura Mag meters cover influent, effluent and recycle duty where the pipework can be opened. Sizing depends on line size and whether the line can be shut down, which is why McCrometer flow meters are selected against your actual pipework.

Leather process chemicals such as syntans, fatliquors, dyes and basic chromium sulphate are outside our range, as is ETP design and construction, including chrome recovery units, belt presses and DAF skids.