Nejayote Wastewater: Acid Dosing and pH Control Equipment
Lime-cooked corn leaves a high-pH, calcium-heavy wastewater. Here is how one California masa plant's upgraded treatment train handles it, step by step, and what equipment each chemical step needs.
Free: HCl Feed & pH Adjustment Sizing Worksheet. The inputs, feed-rate and storage math, and the materials checklist for high-pH food-processing wastewater.
Get the Worksheet →A Central Valley Masa Plant, by the Numbers
Everything in this section comes from one public record: the Central Valley Regional Water Quality Control Board's Tentative Waste Discharge Requirements Order R5-2026-XXXX for a masa plant in Madera County, scheduled for a Board hearing on 22–23 October 2026. The plant is adding a centrifuge, a vermifiltration biological system and a double-lined storage pond, with completion expected by December 2026 (Finding 3). Findings may change at adoption.
Cook water, raised with calcium hydroxide for the masa process
Up to 48 cook batches a day, about 3,500 gallons of water each
Monthly average daily flow limit (76.6 MG per year)
Required at the inlet of the biological (worm-bed) system
What Is Nejayote?
Nejayote is the liquid left over from nixtamalization: dried corn cooked in water with calcium hydroxide (food-grade lime), the step that turns corn into masa for tortillas and chips. Researchers describe it as a highly alkaline (pH 11–12), yellowish, turbid liquid with elevated organic matter, nitrogen and phosphorus (Scientific Reports, 2026). In the example plant, cooking produces about 90–95% of the process wastewater and equipment cleaning the rest, and the cook water sits at about pH 11.0 (Finding 13).
What Lime Does to the Wastewater, and Why Acid Goes In First
Because calcium hydroxide is used in cooking, the influent runs at elevated pH (Finding 15). The order is specific about the acid's first job: "to reduce scaling within the treatment system, wastewater is treated with a solution of hydrochloric acid (HCl) prior to solids removal." Lowering the influent pH helps dissolve calcium deposits and keeps the hydro-sieve working (Finding 16). The same acid also serves as a cleaning agent.
That puts the dose point at the front of the train, on raw, solids-laden, hot, high-pH water. A second pH adjustment happens much later, in the equalization tank, where the target is the biological system's window. They are two different jobs at two different points, and each needs its own metering line and dose-point design.
The Treatment Train, Step by Step
Simplified from the order's findings and its Attachment D flow schematic. Per the schematic's legend, every flow path not marked gravity is pumped.
- 1
HCl dosing · Finding 16
Hydrochloric acid goes into the raw wastewater before solids removal. It dissolves calcium deposits, keeps the hydro-sieve working, and lowers the pH. The acid is stored in a 1,550-gallon double-walled tank.
Equipment: Double-wall acid storage, acid metering pumps, sealless unloading and transfer pumps, corrosion-resistant piping and vented valves
- 2
Hydro-sieve and holding tank · Finding 17
Screens out corn solids, then holds flow in a 5,000-gallon polyethylene tank ahead of a flow meter with a totalizer.
Equipment: Solids-handling transfer pumps, influent flow meter
- 3
Centrifuge · Findings 17, 19
A new centrifuge adds solids separation and drops dewatered solids straight into a trailer. Screw-press filtrate returns to it.
Equipment: Air-operated double-diaphragm or slurry pumps on the solids-laden paths
- 4
Evaporative cooling · Finding 21
A closed-loop cooler brings the wastewater under 100°F without mixing it with the cooling water.
Equipment: Process transfer pumps
- 5
Equalization tank · Finding 22
Flow evens out here, and pH is adjusted as needed to hold the biological system's operating range.
Equipment: pH-trim metering pump (the order doesn't name the trim chemical)
- 6
Worm-bed biological treatment · Findings 20, 23
Two vermifiltration beds of about 33,000 sq ft each. The pilot projected an 81% reduction in BOD and 93% in TSS.
Equipment: Feed and recirculation pumps
- 7
Storage pond and land application · Findings 25–28
About 20 MG, double-lined HDPE pond with a leak collection sump, then metered irrigation to about 353 acres.
Equipment: Submersible sump pump (above the ~8 gpm minimum), irrigation transfer pumps, flow meters
Equalization Tank and the Biological Step
To meet the worm-bed system's operating requirements, influent has to be below 100°F and between pH 6 and 9 (Finding 21). Wastewater from the centrifuge passes through a closed-loop evaporative cooler and then flows to the equalization tank, "where pH adjustments can be made as necessary" (Finding 22). The flow schematic also shows "potential future pH adjustment equipment" after the centrifuge. The order doesn't name the trim chemical, so which chemical, and whether that equipment is in this phase, are design questions to settle before the metering package is specified.
Materials for Hydrochloric Acid Service
What each manufacturer publishes for HCl service. Confirm every line against your delivered concentration and temperature on the submittal.
| Component | Manufacturer data |
|---|---|
| Bulk HCl storage | Poly Processing SAFE-Tank double-wall XLPE, 55–10,500 gal, 110% containment. For HCl service Poly Processing requires a fume-tight manway and venting to a scrubber. XLPE with the OR-1000 liner carries a 5-year warranty, versus 3 years for XLPE alone. |
| Acid metering | Blue-White publishes ratings for 10% and 37% hydrochloric acid for its CHEM-FEED diaphragm pumps (PVDF DiaFlex, diaphragm-failure detection) and FLEXFLO peristaltic pumps. Tube and diaphragm materials are matched to the specified concentration. |
| Unloading and transfer | Finish Thompson sealless plastic pumps. Graco rates FKM, FKM-ETP, FFKM and TFE/P seals "Good" for hydrochloric acid, concentrated included (Husky air-operated double-diaphragm). |
| Piping and valves | Asahi/America's guidance for 37% HCl: PVC with FKM seals, and vented ball valves for off-gas relief. |
Sizing the Acid Feed: Start From a Titration
pH alone can't size an acid feed. pH is a logarithmic snapshot, and the acid a stream needs depends on how much alkalinity it carries, so two streams at the same pH can need very different doses. Take the design dose D from a bench titration of the real wastewater at its worst case. The daily volume of delivered product is then:
F = (Q × D) ÷ (C × SG)
F = gal/day of delivered acid · Q = flow, mgd · D = dose, mg/L as 100% HCl · C = mass fraction of HCl in the delivered product · SG = specific gravity from the supplier's SDS. The pounds form, W = Q × D × 8.34 lb/day of pure HCl, divided by the HCl in one gallon of product (8.34 × SG × C), reduces to the same result.
For a batch plant, the peak matters more than the average. The example plant's limit is 0.21 mgd as a monthly average, but it discharges in up to 48 cook batches a day. Check the feed at peak and minimum flow against the metering pump's rated output and published turndown, then size storage from the delivery cycle and load size.
HCl Feed & pH Adjustment Sizing Worksheet
The 10 inputs to collect, fill-in equations for acid demand, product feed, peak and minimum feed, pump range and bulk storage, plus the HCl materials and containment checklists. Built to hand to a supplier for a one-pass quote.
Get the Worksheet →The Full Supply Scope for This Plant (Free PDF)
We mapped every step of this plant's upgraded train to the equipment LibertyCES supplies, with the order finding behind each figure, so any line can go straight into a basis of design or an "or equal" review. It's open, no email required.
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Submittal-ready cut sheets for any line above, basis-of-design and "or equal" comparisons, and no charge to review a spec before it's issued. See certifications or send a project to the Bid Desk.
Nejayote and High-pH Food Wastewater: Common Questions
What is nejayote?
Nejayote is the wastewater left after corn is cooked in calcium hydroxide (lime) during nixtamalization, the step that makes masa and tortillas. It is highly alkaline, around pH 11 to 12, and carries corn solids and organic load. One California masa plant's tentative discharge order describes its cook water at about pH 11.0.
What does lime do to wastewater?
In a masa plant, the calcium hydroxide used to cook the corn raises the pH of the wastewater and carries calcium into it. The plant in this example doses hydrochloric acid before solids removal to dissolve calcium deposits, control scaling and keep its hydro-sieve working, and the acid lowers the pH at the same time.
Why is acid added before solids removal instead of at the end?
In the example order, the acid's first job is scale control. Hydrochloric acid goes in ahead of the hydro-sieve so calcium deposits don't build up on the screen and downstream equipment. A separate pH adjustment happens later, in an equalization tank ahead of the biological step.
What is an equalization tank for in a food-processing wastewater train?
An equalization tank evens out flow and quality before a treatment step that needs steady conditions. In the masa plant example, wastewater is cooled and then flows to the equalization tank, where pH can be adjusted to hold the pH 6 to 9 range the worm-bed biological system requires.
What pH and temperature does a vermifiltration (worm-bed) system need?
For the system in this example, the tentative Waste Discharge Requirements state that influent must be below 100°F and between pH 6 and 9. The plant meets that with a closed-loop evaporative cooler followed by pH adjustment in an equalization tank. Check the requirements for your own system with its supplier.
How do you size a hydrochloric acid metering pump for high-pH wastewater?
Start from a titration of the actual wastewater, not a pH reading, because the acid you need depends on the stream's alkalinity. Then product feed in gallons per day is flow in mgd times dose in mg/L (as 100% HCl), divided by the delivered acid's mass fraction times its specific gravity. Check the result at peak and minimum flow against the pump's rated range. The free LibertyCES worksheet walks through each step.
Sources. Central Valley Regional Water Quality Control Board, Tentative Waste Discharge Requirements Order R5-2026-XXXX (Madera County masa plant), Findings 2–4, 13, 15–23, 25–28 and Attachment D; findings may change at adoption. Nejayote characterization: Scientific Reports (2026). Equipment data: each manufacturer's published ratings as cited; final selection is confirmed against the project's design documents. LibertyCES prepared this page independently from public records and is not affiliated with the plant, its engineers or its treatment-system vendor.
Sizing an Acid Feed for a Food Plant?
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