Removal of total phosphate and sulfate from industrial wastewater by recirculating flow in nanofiltration

This study is related to industrial wastewater treatment in Indonesia using nanofiltration membrane technology and was carried out on a pilot scale. This research aims to study the total removal of phosphate and sulfate from industrial wastewater through flow recirculation in nanofiltration and the membrane pressure factors that influence the removal of these pollutants. The treated wastewater is industrial wastewater belonging to Jababeka Infrastruktur Corp. and is arranged in various concentrations. The membrane module in this study uses a spiral wound with model specifications NF2-4040 and a two-stage membrane system. The reactor used provides crossflow velocity and is processed by recirculation. The research results stated that variations in concentration and recovery rate provided total removal of phosphate and sulfate in the range of 70-90% and pressure reached 11 bar as both increased. This research has proven that nanofiltration membrane technology can remove total phosphate and sulfate, with the consequence that the more concentrated the wastewater being treated, the greater the pressure required.


Introduction
Industry as a consequence of advances in knowledge and technology requires large resources in the process [1], one of which is water.Clean water is currently a resource that needs to be protected because various pollutants have polluted it.On the other hand, the need for clean water is increasing along with population growth, so the presence of water is very vital in various aspects of life [2].In order to maintain the existence and stability of clean water in the future, various innovations have been created in water treatment, one of which is nanofiltration membrane technology.
Nanofiltration membrane technology has now been widely used on an industrial scale to meet water needs through wastewater recycling schemes [3].In this case, the biodiesel industry is an example of an industry that processes industrial wastewater to meet water needs in the product purification process [4].The next challenge in processing industrial wastewater is the type and concentration of pollutants which are quite high and dangerous if the levels exceed quality standards, one of which is the total phosphate and sulfate.
IOP Publishing doi:10.1088/1755-1315/1307/1/012020 2 Total phosphate is one of the causes of eutrophication in waters if the amount exceeds the capacity of the aquatic environment [5].High concentrations of total phosphate in the body also result in hyperphosphatemia [6].Likewise, sulfate in the form of a mixture with iron dissolved in water will form the metal complex Fe (H2O)6 2+ and is toxic to the human bloodstream [7].However, both total phosphate and sulfate are still needed to meet other needs.Total phosphate is needed to complete the nutrients in fertilizer [8], as well as sulfate [9].Nanofiltration membrane technology in various studies has proven the total removal of phosphate and sulfate in industrial wastewater.NF90 can remove total phosphate up to more than 70% [10], in NF270, total removal can reach more than 90% [11].The increase in total phosphate removal is in line with the increase in membrane performance pressure [10].Likewise, NF270 can remove up to 98% of sulfate along with an increase in membrane performance pressure [12].Based on previous results, this research was conducted regarding industrial wastewater processing in the Jababeka Corp. industrial area using nanofiltration membrane technology and carried out on a pilot scale.This research aims to study the total removal of phosphate and sulfate from industrial wastewater through recirculation flow in nanofiltration membranes and membrane pressure factors that can influence the removal of these pollutants.

Material and Methods
The research was conducted at the Geostech 820 Building (ex-BPPT) of the National Research and Innovation Agency, Serpong, South Tangerang City.The treated wastewater is the effluent from WWTP Phase II Jababeka Infrastruktur Corp., Cikarang, Bekasi.The reactor was assembled to suit the characteristics of industrial wastewater in general, where it is estimated to have high TSS levels, so pretreatment is required to reduce the burden on membrane performance.Providing filter cartridges with a filter size of 10 µm installed in parallel is carried out as a form of pretreatment, so that the performance of the nanofiltration membrane is not severe due to accumulation of TSS.The membrane module used is a spiral wound type with specifications NF2-4040, made from polyamide composite, membrane diameter 4", and membrane length 40" and a two-stage membrane system installed in series.The specifications of the membrane module used are shown in Table 1.The reactor provides cross-flow direction and is processed by recirculation, so that the reject water will return to the reservoir.The diagram of instrument is shown in Figure 1.

Results and Discussion:
Based on experimental results, it was found that nanofiltration membrane technology can remove the concentration of total phosphate and sulfate pollutants.This can be seen through the removal efficiency presented in Figure 2 and Figure 3. Increasing wastewater concentration and recovery rate can reduce the removal efficiency of these two pollutants.The highest total phosphate removal obtained a value of 90.02%, namely in C1R1 (with a total phosphate concentration at the inlet of 1,474 mg/L and an outlet of 0.147 mg/L) and the lowest value obtained a value of 69.91% in C5R3 (with a total phosphate concentration in the inlet and outlet of 3,202 mg/L).0.964 mg/L).The highest sulfate removal obtained a value of 73.95%, namely in C1R1 (with a sulfate concentration at the inlet of 13,989 mg/L and an outlet of 3,644 mg/L) and the lowest value obtained a value of 56.84% in K5R3 (with a sulfate concentration at the inlet of 36,402 mg/L and the outlet of 15,713 mg /L).The removal value for total phosphate when compared with sulfate is much greater, this is because there is a difference in solubility between total phosphate and sulfate.
Both total phosphate and sulfate have different solubility.The solubility of phosphate salts is generally more soluble than some sulfate salts, but this is also influenced by other factors, such as the presence of other ions, pH, temperature.Total phosphate can be dissolved in water, for example phosphoric acid and phosphate salts (such as sodium phosphate and potassium phosphate), while other phosphates such as dicalcium phosphate tend to be insoluble in water.Sulfates that can dissolve in water, for example sodium sulfate and potassium sulfate, while other sulfates such as calcium sulfate and barium sulfate tend to be insoluble in water.
The total phosphate and sulfate that can be removed is the total phosphate that is insoluble in water so that it can undergo the sieving and Donnan exclusion mechanism [14]; [15].The sieving mechanism is based on size, where a membrane with a certain pore size allows smaller molecules to pass through and blocks larger molecules, while the Donnan exclusion mechanism is based on the selective permeability of charged ions.This is caused by differences in ion concentrations on both sides of the membrane.Membranes that have a Donnan exclusion mechanism are more flexible in separating ions based on charge and size [16].Illustrations of these two mechanisms are presented in    In line with the increase in wastewater concentration and recovery rate, as well as the decrease in the removal efficiency of these two pollutants, this also has an impact on increasing pressure on the performance of the nanofiltration membrane.The largest concentration of wastewater and recovery rate, for example (C5R3), can remove total phosphate and sulfate of 69.91% and 56.84% respectively, this causes an increase in pressure which was originally 3.6 bar (at the smallest concentration of wastewater and recovery rate) to increase 3 times fold to 11 bars.This is in line with research [17] that there is a decrease in pressure when there is an increase in sulfate removal.
At a pressure of 11 bar, the concentration of pollutants in the membrane increases significantly, because there is an increase in membrane surface pressure and an increase in the amount of permeate produced, water-soluble cations also have low hydration energy on the surface [17].In this case, the removal of cations, anions, which are mostly phosphate and sulfate ions, passes through the surface of the nanofiltration membrane, so that with 3 times the pressure, the efficiency decreases.The relationship between total phosphate and sulfate removal efficiency and membrane pressure performance is presented in Figure 5.

Conclusions:
Based on the research that has been carried out, it is concluded that nanofiltration membrane technology can reduce the concentration of total phosphate and sulfate pollutants.Increasing wastewater concentration and recovery rate can decrease the removal efficiency of these two pollutants.The highest total phosphate removal was 90.02%, while sulfate was 73.95%.The difference in solubility between total phosphate and sulfate results in differences in the removal values.This also has an impact on increasing pressure on the performance of the nanofiltration membrane, where the pressure increased from originally 3.6 bar increased 3 times to 11 bar.

Figure 5 .
Figure 5.The relationship between total phosphate and sulfate removal efficiency with membrane pressure performance

Table 1 .
The specifications of the membrane module