4.2. Identifying, assessing the wastewater quality of each wastewater stream
4.2.1. Assessing the current state of wastewater quality before treatment by the
Results of wastewater analysis samples of untreated waste are taken at 4 sources of water treatment systems from Hoa Phat Furniture factory.
Electroplating wastewater quality of Hoa Phat Furniture Factory is shown
Table 4.2: Result from qualitative indicator analysis of electroplating wastewater before treatment by the wastewater treatment system of Hoa Phat Furniture Factory
No. Indicators Unit
Result QCVN 40:2011/
BTNMT Column A
NT1 NT2 NT3 NT4
1 pH* - 3.2 (± 0.24) 12.1 (±0.35) 2.12(± 0.12) 7.55 (± 0.28) 6 ÷ 9
2 COD* mg/l 37.025 (±2.03) 801.1 (±55.9) 55.775 (± 0.10) 62.2 (±0.34) 75.0 3 Chromium (VI)* mg/l 375.8 (± 22.89) 92.55 (±8.72) <0.01 <0.01 0.05
4 Nickel* mg/l <0.01 1.47 ±0.48) 4.56 (± 0.33) 49.46 (±1.55) 0.200
6 Chromium (III)* mg/l 181.37 (±9.76) 133.27 (+ 4.37) <0.01 <0.01 0.20
7 Ammonia mg/l 2.23 (±0.017) 1.702 (±0.03) 1.121 1.68 5.00
8 Zn mg/l 1.26 KPH KPH KPH 3.0
9 Fe* mg/l 31.4 (±0.81) 0.245 (±0.025) 0.1 0.07 1.0
10 TSS mg/l 32 30.5 (±0.86) 24 (± 1.73) 20.75 (±1.29) 50
5 Total Mineral oil mg/l 4.0 3.22 (± 0.17) 1.0 4.025 (± 0.44) 5.0
(Source: analysis results)
Where:
NT1: Chromium Wastewater;
NT2: Wastewater processes of chemical detergents (containing NaOH);
NT3: Wastewater electrochemical detergent (containing acid solution);
NT4: Wastewater containing nickel solution, oil;
**: Source: Technical Analysis Department- Environmental and Safety Chemicals center - Institute of Chemical Industry of Vietnam.
The results presented in ftable 4.2 shows the waste water indicators: pH, suspended solids (TSS), total iron (Fe), manganese (Mn), Chromium (Cr), nickel (Ni), COD and mineral oil are exceeding the permissible limits stipulated in column A of QCVN 40:2011/BTNMT for industrial wastewater quality, namely:
pH value
pH of untreated wastewater fluctuates with the widely ranges from the acidic environment (pH 2÷3) to alkaline environment (pH = 9÷11). Waste water source 1, NT1 containing Chromium, and waste water sources3, NT3 (containing acid solution) is an acidic pH environment, pH = 3 and pH = 2.2 is lower than the allowed value between 2/11÷3/46 times specified in column A of QCVN 40:2011/BTNMT for industrial wastewater quality. The pH value of waste water stream 2, NT2 (containing sodium hydroxide solution) equals 11.8, this value is higher than the allowed value about 1.3÷2.1 times.
Because wastewater is both acidic and base, so in the treatment process, depending on the stage, which we must neutralize the acid or alkaline. Neutralizing acid using NaOH, NaHCO3, Na2CO3: This is the simplest method. However, this method is relatively expensive.
Neutralizing acid in water with lime or limestone: This method is simple and highly effective. However, using this method only gets maximum achieve at pH = 7.5 and we have to continue processing the generated solids precipitated after neutralization.
Neutralizing alkaline by H2SO4 and HCl: These are 2 kinds of acid are commonly used to neutralize. This method is highly effective but can be dangerous for workers.
With electroplating waste water, to neutralize the alkalinity, people use H2SO4
solution, to neutralize the acid, people use NaOH at appropriate values.
COD value
Most of the COD value in waste water streams has reached the allowed limits compared with the standard specified in column A of QCVN 40:2011/BTNMT for wastewater quality plating wastewater. Electroplating waste water has little organic materials which are shaded substances, surfactant (oil, grease). Then, COD and BOD of electroplating wastewater are small and not subject to treatment. However, in the waste water stream 2, NT2, COD = 754.9 exceeds the permitted standard about 7 times.
For electroplating wastewater, COD can be treated by phychemical methods: coagulation, flocculation and deposition associated with eliminating residues and suspended substances in water
Chromium value VI (Cr6+)
This is one of the main objects of the waste water treatment system from the electroplating technology. For waste water stream 1, NT1: Chromium wastewater and waste water stream 2, NT2, (containing NaOH), concentration of Cr6+ in the waste stream 1 = 389.8 mg/l and concentration of Cr6+ = 91.2 mg/l in NT2, (exceeding the permissible limits at the source1, NT1 about 3609.2 times and about 844.4 times in the waste water stream 2.
Two streams remaining NT3 (containing acid solution) and NT4 Wastewater stream (nickel solution) meet the allowed standard, which specified in column A of QCVN 40:2011/BTNMT for industrial wastewater quality.
Using PAA and PCA to improve flocculation and sedimentation process, the flocculation process occurs faster.
The electroplating wastewater treatment system from Hoa Phat factory, people use the method: Cr6+ must be reduced to Cr3+ by by taking ion Fe2+
available in wastewater and addition of FeSO4).
All heavy metal ions (Cr3+, Fe3+, Ni2+, Zn2+) will be treated by precipitating with an alkaline solution taking from grease, oil waste water. If the amount of alkali not enough, it will add more NaOH.
Nickel value
The nickel concentration in waste water is very high level, only in the waste water stream 1, NT1, Chromium waste source, the Nickel concentration meets the allowed standards. For the remaining three waste streams, the nickel concentration is very high. The nickel concentration of the waste stream 2, NT2 = 1.0089 ml/g, NT3 = 1.989 ml/g and waste water stream 4 = 46.847 m/l higher than the allowed standards between 1.86÷86.7 times. It is also an object of primary treatment of the wastewater treatment system.
Chromium value III (Cr3+)
Concentration of Cr3+ in water at waste water stream 1 NT1 and waste water stream 2, NT2 = 171.1÷139 mg/l is higher than allowed standard about 129÷159 times. With waster water stream 3, NT3 and NT4, concentration of Cr3+ meets the allowed standard of column A of QCVN 40:2011/BTNMT for industrial wastewater quality.
Fe value
With waste water stream 1, NT1, concentration of Fe is higher than allowed standard about 6 times. With waster water stream 2, NT2, NT3 and NT4, concentration of Fe meets the allowed standard of column A of QCVN 40:2011/BTNMT for industrial wastewater quality.
Zn, Ammonium, total mineral oil, TSS: Meet the allowed standard of column A of QCVN 40:2011/BTNMT for industrial wastewater quality.