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Reference Dosage of Antiscalant (for reference only)
For the primary reverse osmosis system in a desalinated water treatment system, assuming a recovery rate of 75% and operating under 20-50°C, the water quality has a strong tendency to scale. This means an appropriate amount of membrane dispersant must be added to ensure long-term safe and stable operation of the reverse osmosis system and to extend the membrane's lifespan. For the secondary reverse osmosis, where the feed water is the product water from the primary RO, the low hardness and alkalinity mean no antiscalant is needed.
Based on calculations using reverse osmosis-specific software, the recommended dosage at 75% recovery is 3 ppm (based on feed water), and the daily dosage = chemical concentration × feed water flow × 24h ≈ 8.64 kg (assuming feed water flow is 120 m³/h).
PH Adjustment (For Reference Only)
The pH adjustment system uses an X015 diaphragm pump and a 120L water tank. A 0.1%–0.5% NaOH solution is prepared in the water tank and added using the diaphragm pump. The amount of alkali added is adjusted according to the pH and conductivity of the product water to keep the values within a suitable range. The addition concentration is determined based on the actual conductivity of the secondary product water. The diaphragm pump runs synchronously with the secondary reverse osmosis system.
General principles for adjusting alkali addition:
☞ If the conductivity rises sharply, it means too much alkali has been added.
☞ If the conductivity is stable but relatively high, it means too little alkali has been added.
☞ If adding more alkali after initially adding too little causes conductivity to drop sharply but then rise again after a certain point, it means too much alkali is being added.
☞ If the diaphragm pump is at maximum but the desired alkali addition cannot be achieved, the water tank's alkali concentration is too low.
☞ If the pump setting is below 20 and adjustment is too sensitive, the water tank's alkali concentration is too high.
Dosage of Biocide (For Reference Only)
1. Since the raw water is municipal tap water, there are fewer bacteria in the system. However, as the temperature rises, especially in summer, it can affect the normal operation of the reverse osmosis membrane. Therefore, a certain amount of biocide should be added to control bacterial growth and protect the RO membrane from microbial damage. This chemical should be continuously added to the system pretreatment, maintaining residual chlorine in the feed water to inhibit bacterial growth. The dosage should be determined based on the actual level of biological contamination in the system. The recommended dosage is 2 ppm (based on feed water).
2. Daily chemical addition for the desalinated water treatment system = chemical concentration × feed water volume × 24h ≈ 5.76 kg (assuming feed water volume of 120 m³/h).
Addition of Reducing Agent (For Reference Only)
1. To prevent oxidative biocides from entering the reverse osmosis (RO) membrane and oxidizing the membrane elements, a reducing agent dosing system is installed before the RO system. The chemical used is DCL95, and the specific dosage should be determined based on the residual chlorine level in the RO feed water after dosing the oxidative biocide. Generally, it is about 3-5 times the remaining chlorine, with a standard dosing of 2 ppm.
2. The daily dosage for the desalinated water treatment system = chemical concentration × feed water volume × 24h ≈ 5.76 kg (assuming a feed water flow of 120 m³/h). Note that overdosing the reducing agent can also cause system fouling, so regular monitoring of residual chlorine is necessary. This helps adjust the dosage ratio between the oxidative biocide and the reducing agent, ensuring that the reducing agent fully neutralizes the oxidative substances to protect the membrane elements without leaving excess residue that could cause additional contamination in the system.
