Study of the removal of nitrate and dissolved iron pollutants from industrial wastewater to become raw water using nanofiltration

Nowadays, industrial nanofiltration membrane technology is widely used, particularly when it comes to recovering and recycling water for preservation. This research is related to the processing of wastewater from one of the industrial areas in Indonesia into raw water using nanofiltration on a pilot scale. This research aims to identify the removal of nitrate and dissolved iron from industrial area wastewater through flow recirculation in nanofiltration and identify the effect of variations in wastewater concentration and variations in product recovery. The wastewater being treated is wastewater from an industrial area owned by PT. Jababeka Infrastruktur is composed of a ratio of 100% WWTP effluent, 9:1, 8:2, 7:3, and 6:4 between WWTP influent and effluent ratio. This study’s membrane module employs a two-stage membrane system and a spiral wound with model specifications NF2-4040. Recirculation is used in the reactor to process the material and provide cross flow. The results of the study stated that variations in concentration made a significant difference to the removal of nitrate and dissolved iron (p value < 0.05), but variations in product recovery the opposite response. The processed water meets the raw water quality standards for nitrate parameters, but not for dissolved iron parameters at processed water concentrations of 7:3 and 6:4.


Introduction
The worldwide advancement of knowledge of technology brings about continuous growth of industries.One of the essential elements for industrial processes is water [1].However, preserving clear and safe water has become imperative due to pollution from various sources such as industrial, agricultural, and domestic pollution [2].At the same time, as the population grows, so does the demand for clean water, underscoring its significance in all facets of life [3].In order to guarantee the continuity of stability and accessibility to clean water in the future, innovations of technologies such as nanofiltration membrane technology have been developed for water treatment.
The extensive application of nanofiltration membrane technology at the industrial level is now prevalent, especially in addressing water preservation through recovery and recycling [4].According to earlier research, some industries-like the biodiesel sector-use nanofiltration technology to treat industrial wastewater in order to meet the water requirements for the purification process of their products [5].The second challenge in treating industrial wastewater is dealing with high concentrations of dangerous pollutants, like dissolved iron and nitrate, which can be dangerous if they exceed set quality standards.
Increased nitrate levels in water can result in widespread algal growth, eutrophication, and adverse health effects on humans, such as methemoglobinemia, diabetes, and cancer [6].On the other hand, iron is essential to human health, yet the rise in the concentration of iron ions in lead to undesirable effect like discoloration and odor to water if surpass quality standard [7].In water, iron appears in dissolved form as divalent ion (Fe 2+ ), trivalent ion (Fe 3+ ), or complexes.In the presence of dissolved oxygen, Fe 2+ can readily be oxidized to Fe 3+ , causing precipitation as hydroxide causing the mentioned problem [8].Consequently, treating these pollutants prior to their release into the environment is crucial.
Several previous studies proved that nanofiltration can efficiently remove nitrate and dissolved iron from industrial wastewater.The study [9] indicated that a high-performance nanofiltration membrane was efficiently able to remove dissolved iron and other heavy metal ions including Fe 2+ , Pb 2+ , Ni 2+ , Mn 2+ , Zn 2+ , Cu 2+ with percentage rejection of 99.88%, 99.61%, 99.51%, 99.31%, 99.11%, 98.72% respectively.The previous study [10] indicated that the nitrate pollutant was efficiently removed with a 90.5% efficiency value by nanofiltration treatment with a pore size of 0.4 nm.This research is related to the processing of wastewater from one of the industrial areas in Indonesia into raw water using nanofiltration on a pilot scale.

Material and Methods
The National Research and Innovation Agency's Geostech 820 Building (ex-BPPT), located in Serpong, South Tangerang City, served as the research site.The treated wastewater comes from PT. Jababeka Infrastruktur's WWTP Phase II in Cikarang, Bekasi.The reactor was made to specifically meet these needs because industrial wastewater typically has high TSS levels and pretreatment is required to reduce the strain on membrane performance.Installing filter cartridges with a 10 µm filter size in parallel achieves pretreatment.With specifications NF2-4040, the membrane module is spiral wound and uses a two-stage membrane system that is put in series.It is constructed of polyamide composite, has a membrane diameter of 4", a membrane length of 40", and is employed.Recirculation and cross-flow direction provided by the reactor, which processes the reject water and returns it to the reservoir.Figure 1., depicts an illustration of the reactor.The wastewater being treated is wastewater from an industrial area owned by PT.Jababeka Infrastruktur is composed of a ratio of 100% WWTP effluent, 9:1, 8:2, 7:3, and 6:4 between WWTP influent and effluent ratio.The product recovery, or the volume of permeate produced by the membrane processing system relative to the volume of feed water supplied to the system, can be systematically computed using Equation 1.
Rejection can be systematically calculated using Equation 2. to gauge the membrane's ability to pass or hold onto dissolved chemicals.
where Cp is the treated water's concentration value and Co is the feed water's concentration value [13].Samples are taken at the reservoir (inlet) and after they have passed through the membrane (outlet) in order to measure the amounts of nitrate and dissolved iron.Nitrate which is in an acidic environment (pH 2.0 -2.5) due to brusine sulfate reacts with sulfanilic acid to form a yellow complex compound, based on SNI 06-2480-1991.Then, iron (III) will be reduced to iron (II) by adding hydroxylamine chloride and adding orthophenonthroline to form an orange, based on SNI-06-4138-1996.

Results and Discussion:
Nanofiltration membrane technology has been proven to be able to remove nitrates and dissolved iron.Based on Figure 2., represents the nitrate removal efficiency whereby the highest nitrate removal efficiency of 68.05% found in K1R1 involves a combination of 100% effluent water concentration with a 40% return rate.Conversely, the lowest efficiency value of 52.80% occurs in K5R3, with a 6:4 concentration variation and 80% return rate.A probability value below 0.05 (p value ≤ 0.05) indicates that nitrate removal was significantly impacted by the treatment with variation in concentration.The probability value above 0.05 (p value > 0.05) did not, however, result in any appreciable variations in nitrate removal due to variation in intersection.Nitrate is a pollutant that tends to have a negative charge, so the Donnan exclusive mechanism can work in this case in conjunction with the filtering mechanism [13].Based on Figure 3., represents the removal of dissolved iron from the industrial wastewater of PT.Jababeka Tbk, on which the maximum removal efficiency of 45.02 occurs in K1R1 (a combination variation of 100% concentration of effluent water and 40% return rate), while the lowest value of 15.74% found in K5R3 (a combination variation 6:4 of concentration with 80% return rate).When treating 100% concentration of effluent water, there is no significant difference in iron dissolution between concentrations of 9:1 and 8:2 (p value > 0.05).However, there is a significant difference at the concentration of 7:3 and 6:4 (p value ≤ 0.05).Therefore, the treatment variation does not show a significant difference in the removal of dissolved iron when considering o concentration with a p value greater than 0.05 (p value > 0.05).

Fig 3. Removal of dissolved iron
In comparison, nitrate has a high removal efficiency to dissolved iron which may be caused by the difference in particle size between them.Dissolved iron tends to exhibit a positive correlation which makes it more challenging to exclude the Dannon mechanism in nanofiltration membrane technology [14].Because both nitrate and dissolved iron are insoluble in water, they can be eliminated through sieving and the Donnan exclusion mechanism [14].The Donnan exclusion mechanism is based on the selective permeability of charged ions, whereas 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.The ion concentrations on either side of the membrane differ, which is the cause of this.Ions can be separated more easily by membranes with a Donnan exclusion mechanism based on size and charge [14].

Conclusions:
It is concluded from the conducted research that nitrate and dissolved iron concentrations can be decreased using nanofiltration membrane technology.The removal efficiency of these two pollutants can be reduced by increasing the concentration and product recovery of wastewater.Iron that had been dissolved was 45.98%, while the maximum nitrate removal was 68.05%.Variations in the solubility of dissolved iron and nitrate lead to variations in the removal values.Changes in concentration had a significant impact on the removal of dissolved iron and nitrate (p value < 0.05), while changes in product recovery had the opposite effect.At processed water concentrations of 7:3 and 6:4, the water satisfies the requirements for dissolved iron but not for nitrate parameters, which are part of the raw water quality standards.

Figure 4 .
presents illustrations of these two mechanisms.