Choosing PAC Grade: 27%, 28% or 29% for Your Water Treatment Train

Reagent selection is a technical decision, not an afterthought

Water treatment design tends to focus on the headline units: the separator, the oxidation reactor, the membrane bank. Yet the flocculant chosen upstream can quietly decide whether those units perform as specified. Polyaluminium chloride (PAC) is the most widely used inorganic polymer flocculant in the field, and its single most important specification is the aluminium oxide content — the fraction that governs purity, flocculation activity, dose required and where the product can sensibly be applied.

Across industrial wastewater, municipal sewage and advanced treatment work, SINOKLE has found that the three mainstream content grades behave less like a purity ladder and more like instruments of different resolution. Each is matched to a particular water quality, discharge standard and cost constraint rather than being universally better than the grade below.

What actually changes between the grades

Everything follows from the Al2O3 proportion. Raising the content reduces iron, calcium and water-insoluble matter, strengthens flocculation activity, lowers the dose needed for the same result and cuts sludge volume — while raising the unit price. Reading the three grades in that light makes their roles obvious.

• The economical grade is the industrial workhorse, usually drum-dried. It is cheap, flocculates quickly and tolerates high-turbidity water unusually well, which makes it the default under a cost-first strategy.
• The balanced grade sits at the market's centre of gravity, trading a little purity for a stable price and delivering consistent performance across the widest range of routine duty.
• The high-purity grade is spray-dried, with very low insoluble matter and heavy metal content well inside the national standard. It delivers the highest flocculation efficiency and the smallest sludge volume, and exists for the cases where effluent safety is the binding constraint.

Going from the low grade to the high grade is a journey from economical coarse treatment toward high-standard fine treatment. Position on that spectrum is a design decision, and SINOKLE sets it according to project objectives before any dosing point is fixed.

How the grades are actually sequenced in practice

When SINOKLE engineers compare grades side by side in project notes, the shorthand often appears as 1.27%PAC, 2.28%PAC and 3.29%PAC — that is, the 27%PAC, 28%PAC and 29%PAC products listed in sequence. The apparent decimals are numbering artefacts from the way the options are catalogued, not different products, and reading them that way prevents a costly mis-order.

Where the 27%PAC grade earns its place

The low grade targets high-turbidity front-end duty and cost-sensitive projects, where the job is to remove large volumes of inorganic suspended solids quickly.

Sour water pre-treatment in refining and petrochemicals is a good example. Coking sulfur-containing wastewater carries a high load of coke powder at 10–20μm alongside emulsified oil, and coarse coagulation ahead of the core CDFU or KHC coalescing separator strips most suspended solids and protects the precision units downstream. Mining and building-materials streams such as coal-washing wastewater and tailings slurry are another fit: the objective is solid-liquid separation at the lowest cost, and large dense flocs that settle fast deliver it. Emergency dosing when influent quality at a plant swings abruptly, and sludge conditioning before dewatering, round out the list.

Where the 28%PAC grade becomes the default

The middle grade is what SINOKLE uses most often in industrial advanced treatment and municipal upgrading, because stable performance is what keeps a whole system inside its permit month after month, across COD, suspended solids and colour.

After a CDOF ozone catalytic oxidation step, refractory organics are broken into smaller molecules but colour and fine suspended solids can remain. Dosing an appropriate amount of 28%PAC, typically 15–30ppm, flocculates that residue so the outlet is genuinely clear. In a secondary CDFU treatment unit that extends an existing dissolved-air flotation (DAF) stage at a wastewater treatment plant, a small dose raises removal of emulsified oil and colloidal matter while cutting scum production. Industrial circulating water and reclaimed-water reuse are the third common duty, where the target is suspended solids and algae in cooling circuits or advanced flocculation of biologically treated effluent for landscaping and flushing.

Where the 29%PAC grade is the only sensible choice

The high-purity grade comes into play when the project objective is drinking water safety, electronic-grade ultrapure water or zero liquid discharge. Its very low impurity content is what removes the risk of introducing secondary pollution at the last step.

Municipal waterworks and direct drinking water systems use it in the flocculation stage to pull trace colloids, organics and heavy metals from raw water. At the front end of high-purity production in electronics, semiconductors and pharmaceuticals, 29%PAC protects expensive reverse osmosis and ultrafiltration membranes from fouling and blockage. Zero liquid discharge projects with strict limits on residual ions use it for final polishing before the water reaches evaporation and crystallisation.

The SINOKLE selection model

SINOKLE works from a multi-dimensional model rather than experience alone. Diagnosis of the water comes first: influent turbidity, organic composition, oil-bearing characteristics, salinity and pH value. High turbidity and high suspended solids point toward the low grade; advanced treatment of complex organic wastewater points to the middle; low turbidity with high safety requirements points to the high grade.

The outlet standard then narrows the field. Compliant discharge generally allows the middle grade, while reuse to high quality or any application touching human health pushes the decision to the top grade. Life-cycle cost accounting follows, comparing not only reagent unit price but the total dose needed to reach the same target, the sludge disposal cost and the effect on membrane service life — a higher-purity product with a higher unit price frequently delivers the lower overall operating cost. Finally, dosage point and dose are validated inside the SINOKLE patented processes, including CDFU and CDOF, so that chemical coagulation, physical separation and advanced oxidation work with each other rather than at cross purposes.

The point is not that one grade beats the others. It is that value comes from matching the specification to the duty, and that a decision made on that basis turns each unit of reagent cost into measurable treatment performance.