Air flotation-biochemical treatment of high concentration printing ink wastewater (I)

Abstract: In view of the characteristics of high concentration of dyestuff and printing ink, high concentration of CODcr, this paper proposes a treatment process that adopts air flotation for pretreatment and then integrates domestic sewage with biochemical treatment. It has been proved by practice to be reasonable.

Keywords: ink heat stability oxidizer aeration

1 Introduction

In recent years, the ink industry has developed rapidly. The pigments used in inks generally have light and heat resistance stability, acid resistance, alkali resistance, resistance to common oxidants, and have good coloring power, hiding power and sublimation fastness. The commonly used phthalocyanine pigments have many types, bright color, strong coloring power, good fastness, and are widely used in paints, inks and so on. In the printing production process, there will be high-color ink wastewater, and the waste water will be discharged intermittently. The water quality and water volume will change greatly with time, which will make it more difficult to design and operate the wastewater. Printing ink wastewater treatment methods are many, there are many physical and chemical treatment methods, biological methods. The actual water treatment project is often a combination of multiple methods in order to achieve the best results. In this example, the air flotation-biochemical method was selected to treat high-concentration printing ink wastewater and achieved good results.

2 Project Overview

2.1 The status of the study and the choice of treatment methods

A joint venture company in Guangzhou has a carton production line with a production capacity of 4 million cartons per year. There are also dining halls, industrial boiler rooms and tank farms. The wastewater generated by the project includes printing wastewater, canteen wastewater, oil tank wastewater and employees' domestic wastewater. The printing waste water is derived from the printing process of cardboard and the cleaning of printing machinery and equipment. This type of waste water contains a large amount of water-soluble ink with an external discharge of 20t/d, containing SS, CODcr, BOD5, color, oil and other pollutants. The oil concentration can reach 167mg/l, and the CODcr can reach as high as 18200 mg/l. The components are complex and the concentration is high. In addition, the staff canteen discharges about 50 t/d of restaurant wastewater daily, containing large quantities of oils, food residues and suspended solids; domestic sewage comes from the employees' living processes, including the employees’ showers, laundry, etc., and the total discharge of canteens and domestic sewage. About 100 t/d, the quality of domestic sewage has a large range of fluctuations in water content, which contains more organic matter and a higher content of surfactants. In addition, the company's oil tanker oil from the pipeline to run leaking oil and residual oil tank cleaning effluent, mixed with rainwater, there is a small amount of washer water, mainly containing a small amount of caustic soda and cassava flour and other impurities. (See Table 1 for wastewater quality details)

As the company is a joint group company, in addition to high-concentration printing ink waste water, there is a certain amount of domestic sewage, so use the flotation-biochemical method to treat the company's comprehensive wastewater. Taking into account the characteristics of ink waste water and other sewage water, low concentration, high concentration, and complex composition, air flotation is used for pretreatment to reduce the subsequent processing load. In addition, the air floatation method is affected by the temperature and is suitable for intermittent operation. It is small in area, easy to manage, and flexible. It is suitable for the printing wastewater treatment requirements of the company. Therefore, we first use the air floatation process to treat the production wastewater, and then we can use it together with the canteen wastewater. The domestic sewage is treated together with biochemical treatment to comprehensively solve the problem of several types of wastewater treatment produced by the company.

Table 1: Design Wastewater Quality Unit Unit Raw Water Before Treatment of Ink Wastewater Ph 6.78~6.86
SS mg/L 132～5088
CODcr mg/L 1380～18200
BOD5 mg/L 544～7600
Oil mg/L 110～167
NH3-N mg/L 48.1 to 1067
Chroma 1000 to 4000
Before domestic wastewater treatment Ph 7.07～7.94
SS mg/L 31~386
CODcr mg/L 82~366
BOD5 mg/L 31.1~175
Oil mg/L 57.8～62.4
NH3-N mg/L 7.34 to 7.62

2.2 Process flow

Integrated wastewater treatment engineering process see Figure 1.
Filtered water Sludge drying field → Mud cake washing machine water ↓ Pump slag ↑ ↑ Sludge ink waste water → Mechanical grating machine → Conditioning tank → Air flotation device → Inclined pipe sedimentation tank
Tank area oil sewage supernatant ↓
Domestic sewage grid submersible pump Manure sewage → Septic tank → → Anaerobic pre-treatment → A-level aeration tank → A sedimentation tank → Class B aeration tank → Secondary sedimentation tank → Filter tank → Drainage canteen sewage → Oil separation Slag pool → conditioning pond ↑ ↑
Fan

Figure 1: Process Flow Diagram

Printing ink waste water, production, and oily wastewater are first passed through a mechanical grate machine to remove large solid impurities, and then transferred into a conditioning tank for homogenization, adjusting the amount of water and water quality, and then pumped up to an air flotation device. The flotation device is equipped with a drug in front of it. In the system, the mixture is added and the solid-liquid separation is carried out. The waste water enters the sedimentation tank again. The sludge is separated and dried in the sludge drying field. The pretreated wastewater and the living and canteen wastewater are initially processed in an anaerobic conditioning tank. Treatment, and then enter the two aeration tank for aerobic treatment, residence time 6 ~ 7h, biodegradation, and further increase the removal rate of CODcr, BOD5. The sludge generated by the biochemical system is sucked into the anaerobic conditioning pool by a suction dredge, and the sludge in the decomposition system is digested by microorganisms to reduce the sludge displacement.

2.3 Major Structures and Equipment

2.3.1 Air floatation device

Air flotation is based on micro-bubbles, which causes flocs and micro-bubbles formed by fine particles in the wastewater to adhere, thereby reducing the apparent density of the floe and allowing it to float by means of buoyancy, thereby achieving forced floating of the floc and achieving solid-liquid separation. , Purification of wastewater. The air flotation device occupies only 6 square meters and the processing volume is 5 m3/h.

2.3.2 Anaerobic conditioning tank

Its main function is to collect wastewater for homogenization and to generate anaerobic hydrolysis reaction, initially decompose organic pollutants, and precipitate suspended solids to facilitate later-stage biochemical treatment.