A. Introduction
In water treatment, deionizer resin is important in removing mineral ions dissolved in water. These resins generally have a lifespan of five to ten years and require careful maintenance to remain efficient.
Image 1: Deionization resin filtration layout
However, several factors can shorten the life of the resin. These factors include iron and manganese content, aluminum, hardness, oil content, silica, microbes, and oxidation that can damage the resin.
The resin regeneration process is carried out to extend the life of the deionizer resin by restoring its absorption capacity. To maintain efficiency, the demineralization process must be able to reduce the conductivity value of water by at least 80-85%.
TDS of water samples based on EC analysis values can be calculated using the following equation:
TDS (mg/l) = 0,5 x EC (dS/m or mmhos/cm)
TDS (mg/l) = 0,5 * 1000 x EC (mS/cm)
High Total Dissolved Solids (TDS) in feed water will affect the regeneration frequency, so the higher the TDS, the faster the resin is saturated and requires regeneration.
Resin regeneration uses chemicals such as HCl or H2SO4 and NaOH, the use of which depends on the amount of resin that needs to be regenerated. The more often the regeneration cycle is carried out, the higher the costs required.
Here is the reaction of the resin regeneration process:
Ca – Resin + 2HCl → 2H – Resin + CaCl2
Cl – Resin + NaOH → OH – Resin + NaCl
SiO3 – Resin + 2NaOH → 2OH – Resin + Na2SiO3
B. Discussion
Effect of Coagulant on Deionization (DI) Resin Efficiency
Aluminium Sulphate (Al₂SO₄), Poly Aluminium Chloride (PAC), and Aluminium Chlorohydrate (ACH) are chemical coagulants that are often used in water treatment to help precipitate fine particles.
However, their use must be appropriate, because excessive doses or inappropriate use can reduce the efficiency of deionization resins. If the precipitated particles are not removed properly, they can clog or settle on the surface of the resin and reduce its capacity and efficiency.
Chemical coagulants can affect or change water characteristics such as pH and TDS, which will then affect the performance of deionization resins.
Table 1: Comparison of chemical coagulants Aluminum Sulphate, Poly Aluminum Chloride (PAC), and Aluminum Chlorohydrate (ACH)
Aluminium Based |
Parameter | Alum | PAC | ACH |
Price | Cheap | Relatively Cheap | More Expensive |
Corrosivity | Less Extreme | Less Extreme | Less Extreme |
pH Decrease | High | Medium | Low |
Consume Alkalinity | High | Moderate | Low |
Dosage Control | Easier | Easier | More Difficult |
Character Floc | Small and Solid | Small and Solid | Small and Solid |
Sludge Generation | Medium | Medium | Low |
Colouring Effects | None | None | None |
Using chemical coagulant Aluminium Chlorohydrate (ACH) does not cause a significant decrease in pH, so the consumption of alkali for pH adjuster becomes small. With this condition, the increase in TDS in water will also be small.
Use of ACH in State-Owned Enterprises in Dumai-Riau
In one of the clean water treatment units in a state-owned company in Dumai-Riau, which uses peat water (colored) raw water, a change was made from the coagulant Aluminum Sulphate to Aluminum Chlorohydrate (ACH).
Previously, this company used Aluminum Sulphate (alum), but with ACH (Hinco Alpha), better results can be obtained with lower doses and without the need for alkali injection to adjust the pH.
Photo 1: Raw Water
Testing Through Jar Test
The jar test is one of the methods often used in the water treatment process to determine several things, such as:
- Determining chemical dosage
- Determining chemical injection sequence
- Optimizing treatment process performance
- Solving treatment process operational problems
- Evaluating different treatment schemes.
To determine the best chemicals to be used for the clean water treatment process, a jar test was conducted. From the results of the jar test, the following results were obtained:
Table 2: Jar test results for chemical coagulants Aluminum Sulphate, Poly Aluminum Chloride (PAC), and Aluminum Chlorohydrate (ACH)
Through jar tests, the optimal dosage for each coagulant was determined:
- ACH (Hinco Alpha): Optimal dose of 35 ppm without significantly affecting pH.
- PAC (PCO 04): Optimal dose of 42 ppm, but requires the addition of pH adjuster (NaOH) of 14 ppm because it lowers pH.
- Aluminium Sulphate (Al₂SO₄): Optimal dose of 70 ppm and also requires NaOH of 16 ppm for pH adjustment.
Of the three coagulants, ACH has the lowest impact on increasing conductivity, which is critical in maintaining the efficiency of the deionization resin.
Table 3: Results of jar test of chemical coagulant and total chemical cost
| No | Chemical Water Treatment | Total Cost Chem. Water Treatment / m3 |
| Coagulant | Flocculant | Chem. pH Adjuster |
| Type | Dosis (mg/L) | Type | Dosis (mg/L) | Type | Dosis (mg/L) |
| 1 | Alum | 70 | PA 214 | 0.6 | NaOH | 16 | Rp 397 |
| 2 | PAC | 42 | PA 214 | 0.6 | NaOH | 14 | Rp 421 |
| 3 | ACH | 35 | PA 214 | 0.6 | NaOH | 0 | Rp 331 |
Automatic Injection Application with ACH (Hinco Alpha)
Based on the results of the jar test conducted, the chemical coagulant ACH (Hinco Alpha) only uses a smaller dose and does not cause a significant decrease in water pH. Alkali injection is not required as a pH adjuster because of the small decrease in pH.
Image 2: Layout of the clean water processing process of a BUMN Company in Dumai-Riau Province
To improve the efficiency of coagulant injection, the company uses an automatic injection system equipped with a Streaming Current Monitor (SCM). SCM automatically regulates the coagulant injection dose based on needs, reducing human error and ensuring the stability of the quality of the processed water.
Image 3: Coagulant auto-injection layout
Some of the advantages of using SCM for chemical coagulant injection:
- Reduce human error
- Increase coagulant injection efficiency
- Automatic monitoring that provides real-time information
- Speed up decisions in solving problems
- Prevent processing problems with alarm, trending, and historical record features.
The ACH (Hinco Alpha) chemical coagulant injection process with this automatic system can produce stable treated water quality according to the established standards.
Photo 2: Treated Water
The quality of treated clean water is getting better after using ACH (Hinco Alpha) as a chemical coagulant in the clean water treatment process. Alkali injection (pH adjuster) is not necessary because the pH decrease is small. And the increase in conductivity in treated water is also small. Chemical coagulant ACH (Hinco alpha) also produces good performance for removing turbidity, color, organic, and TSS.
Table 4: Performance treatment chemical coagulant Aluminium Chlorohydrate (ACH)
Resin Regeneration Cycle Savings
When using Aluminum Sulphate, the resin regeneration cycle was carried out every 17 hours, with an average of 42.3 times a month. After switching to ACH (Hinco Alpha), the regeneration cycle was extended to every 27 hours, with an average of only 26.6 times a month.
With a decrease of 15 regeneration times per month, the chemical requirement for resin regeneration is also reduced, which means a significant cost reduction in the regeneration process.
C. Conclusion
The use of chemical coagulant ACH (Hinco Alpha) in one of the water treatment units of a state-owned company in Dumai-Riau, can reduce the frequency of resin regeneration and significantly reduce the cost of the clean water treatment process. In addition, the stability of clean water quality can be maintained without the need for additional pH adjustments, and the minimal increase in conductivity helps maintain the efficiency of the deionization resin.
