What Is the Best Wastewater Treatment Process?

Sewage treatment process ^[1] is a variety of economic, reasonable, scientific and effective process methods for urban domestic sewage and industrial wastewater. Sewage treatment is widely used in various fields such as construction, agriculture, transportation, energy, petrochemicals, environmental protection, urban landscape, medical treatment, catering and so on. The urban sewage treatment process should be determined after a comprehensive technical and economic comparison based on the treatment scale, water quality characteristics, environmental functions of the receiving water body, and local actual conditions and requirements.

Under normal circumstances, actual sewage often contains multiple pollutants, and a single treatment method often cannot achieve the expected results. In order to obtain a better treatment effect at a lower treatment cost, it is often necessary to adjust several treatment techniques and methods according to a number of factors based on the quality of the sewage, the amount of water, the degree of treatment, the possibility of recovering useful substances, and the conditions of the fund site The primary and secondary relationships and the order of the front and back are reasonably combined to form a complete purification treatment system ^[2]

The type of domestic sewage treatment process not only determines the sewage purification effect, but also determines the amount of sludge produced in the sewage purification process and the sludge treatment method ^[3]

1) The urban sewage treatment process should be determined after a comprehensive technical and economic comparison based on the treatment scale, water quality characteristics, environmental functions of the receiving water body, and local actual conditions and requirements.

2) The main technical and economic indicators for process selection include: treatment of unit water investment, reduction of unit pollutant investment, treatment of unit water consumption and cost, reduction of unit electricity consumption and cost, floor area, operational performance reliability, management and maintenance Difficulty, overall environmental benefits, etc.

3) The quality of sewage influent should be determined realistically, and process design parameters should be optimized. It is necessary to conduct a detailed investigation or measurement of the current water quality characteristics and pollutant composition of sewage, and make reasonable analysis and prediction. When the water quality composition is complex or special, a dynamic test of the sewage treatment process should be carried out, and a pilot study should be carried out if necessary.

4) Actively and prudently adopt efficient and economical new processes. For the first application of new technology in China, it must be tested and produced, and reliable design parameters must be provided before application. ^[1]

Classification of "Water Pollution Control Engineering"

Separation technology of insoluble pollutants :

1. Gravity settlement:

Modern sewage treatment technology can be divided into primary, secondary and tertiary treatment according to the degree of treatment.

The primary treatment mainly removes solid pollutants in suspended state in the sewage. Most of the physical treatment methods can only meet the requirements of the primary treatment. After primary treatment, BOD can be removed by about 30%, which can not reach the discharge standard. The primary treatment belongs to the pretreatment of the secondary treatment.

The secondary treatment mainly removes colloidal and dissolved organic pollutants (BOD, COD substances) in sewage, and the removal rate can reach more than 90%, so that the organic pollutants reach the discharge standard.

Tertiary treatment, further treatment of refractory organics, nitrogen and phosphorus can cause

Process flow

Raw water grille conditioning tank lift pump bioreactor circulation pump membrane module disinfection device reclaimed water tank reclaimed water system

MBR sewage treatment process description

The sewage enters the adjustment tank through the grille and enters the bioreactor through the lift pump. The aerator is oxygenated through the PLC controller. The effluent from the bioreactor enters the membrane separation processing unit through the circulation pump. The concentrated water returns to the adjustment tank and the water separated by the membrane After rapid mixing and chlorination disinfection (sodium hypochlorite, bleaching powder, chlorine tablets), enter the water storage tank. The backwash pump uses the treated water in the washing tank to backwash the membrane treatment equipment, and the backwash sewage returns to the adjustment tank. The opening and closing of the lift pump is controlled by the water level in the bioreactor. The filtration operation and backwash operation of the membrane unit can be controlled automatically or manually. When the membrane unit needs chemical cleaning operation, close the water inlet valve and the sewage circulation valve, open the medicine washing valve and the medicine circulation valve, start the medicine liquid circulation pump, and perform the chemical cleaning operation.

MBR process characteristics

Membrane biological treatment technology applied to wastewater recycling has the following characteristics:

(1) The solid-liquid separation can be performed efficiently, and the suspended matter, colloidal matter, and microbial flora lost in the biological unit in the wastewater can be separated from the purified water. The separation process is simple, the floor area is small, and the quality of the effluent is good. Generally, it can be reused without third-level treatment.

(2) The biomass in the biological treatment unit can be maintained at a high concentration and the volume load can be greatly improved. At the same time, the efficiency of membrane separation can greatly reduce the hydraulic retention time of the treatment unit and reduce the footprint of the bioreactor accordingly.

(3) As it can prevent the loss of various microbial flora, it is conducive to the growth of slow-growing bacteria (nitrobacteria, etc.), so that various metabolic processes in the system proceed smoothly.

(4) Make the residence time of some large molecules difficult to degrade organic matter longer, which is conducive to their decomposition.

[5] Membrane treatment technology is the same as other filtration and separation technologies. During long-term operation, the membrane is blocked as a filter medium, and the membrane's running time is gradually reduced by the amount of water. Effective backwashing and chemical cleaning can slow the membrane flux To reduce the effective life of the MBR system.

(6) MBR technology is applied in urban sewage treatment. Due to its simple process and convenient operation, it can realize fully automatic operation management.

SBR process

summary

The SBR wastewater treatment process is a sequential batch activated sludge process, which is called the Sequencing Batch Reactor Activated Sludge Process.

Referred to as (SBR-Sequencing Batch Reactor) intermittent activated sludge wastewater treatment process, SBR process.

It is based on a wastewater biological treatment activated sludge process that degrades organic matter, ammonia nitrogen and other pollutants in sewage under aerobic conditions by microorganisms growing in suspension. Sewage treatment technology that is widely accepted and adopted around the world to operate in intermittent aeration mode to change the environment in which activated sludge grows.

Process flow

A representative SBR

Process flow

The choice of hospital sewage treatment process is the key to hospital sewage treatment design. Whether the process is reasonable will directly affect the treatment effect, project investment, operating costs, and management safety. The determination of the process flow is based on factors such as the nature of the hospital, treatment requirements, fate of sewage, and technical and economic conditions. The basic principles are:

1. Determine the level of hospital sewage treatment according to the discharge direction and treatment requirements of hospital sewage. If the hospital sewage is discharged into urban sewers, according to the requirements of "Water Quality Standard for Sewage Discharged into Urban Sewers" and "Hospital Wastewater Discharge Standard", a primary treatment and disinfection process can be adopted. If the sewage is directly discharged into the surface water body, it shall be treated in accordance with the requirements of the "Integrated Sewage Discharge Standard", and usually requires a secondary treatment and disinfection process. If there are special requirements, even a tertiary treatment process is needed, such as in tertiary terrestrial waters or sewage reuse outside the secondary protection area of the water source.

2. According to the difference between the elevation of the hospital sewage discharge outlet and the elevation of the city sewers connected to it, determine whether to use the self-discharge or lifting disinfection process. When the height difference is greater than 600mm, a siphon fixed-ratio self-disinfection process can be adopted. When the height difference is small, an ultrasonic automatic fixed-ratio chlorine-disinfection process or an elevated fixed-ratio chlorine-disinfection process can be used.

3. Choose the type of disinfectant according to the nature, scale and technical and economic conditions of the hospital. General medium and large hospitals recommend the use of liquid chlorine disinfection process. Sodium hypochlorite disinfection can be used in densely populated areas. Conditional infectious disease hospitals can use ozone disinfection technology, small hospitals can use chlorine disinfection technology. 4. Radioactive wastewater, heavy metal wastewater and other special wastewaters should be treated accordingly. For example, the radioactive wastewater should be treated with old decay storage tanks. The heavy metal wastewater can be treated by chemical method or ion exchange method. The hospital sewage treatment process is as follows:

First-level processing flow

The primary treatment of hospital sewage treatment usually includes septic tanks, sedimentation tanks, double-layer sedimentation tanks or conditioning tanks. In some simple hospital sewage treatment, some do not set up sedimentation tanks and conditioning tanks, but use septic tanks as primary treatment facilities. The septic tank effluent directly enters the chlorination contact tank through the grid, the quantitative tank (or the water collecting well).

Second and second stage processing flow

When the effluent from the primary treatment of hospital wastewater cannot meet the water quality requirements of the discharge standard, a secondary treatment process is usually used, which removes organic pollutants such as BOD5, COD, phenol, and LAS from the hospital wastewater through biological treatment. The effluent quality of the secondary treatment is improved, the amount of disinfectant can be reduced, and the disinfection effect can be improved. The secondary treatment methods used in hospital medical water include biological contact oxidation method, biological turntable method, tower biological filter method, jet aeration method and oxidation ditch method.

Third, the general process of hospital sewage treatment

In addition to the treatment and disinfection of bacteria-containing sewage, the hospital's sewage treatment system should also separately treat various special drainage, such as wastewater containing heavy metals, radioactive wastewater, oily wastewater, and printing wastewater. Heavy metal wastewater comes from dental treatment and laboratory, and contains harmful pollutants such as mercury and chromium, which can be treated by chemical precipitation method or ion exchange method. Radioactive wastewater comes from isotope treatment and diagnosis. Low-concentration radioactive wastewater is treated with a decay cell or chemical co-precipitation method and ion exchange method. Oily wastewater comes from the kitchen canteen and is generally treated with an oil trap. The printing wastewater comes from photo printing and contains harmful substances such as silver, developer, and fixing agent. The silver-containing wastewater can be recovered by electrolysis, and the developer can be treated by chemical oxidation.

MBR hospital wastewater treatment process

MBR is a new wastewater treatment process that combines membrane separation technology with a bioreactor. Compared with the secondary sedimentation tank in the traditional activated sludge process, the solid-liquid separation can be performed efficiently, which overcomes the disadvantages of the unstable effluent water quality and the easy expansion of sludge in the traditional process.

Advantages of MBR:

Strong anti-shock load capacity, high quality and stable effluent water quality, can completely remove SS, and has a good retention effect on bacteria and viruses

The complete separation of sludge age (SRT) from the hydraulic retention time (HRT) of the reactor makes the operation control more flexible and stable; the concentration of microbial biomass in the bioreactor can be as high as 10 g / L or more, the volume load of the processing device is high, and the floor area Small, reducing the volume required for nitrification

MBR has low residual sludge production and even no residual sludge discharge, reducing sludge treatment costs

It is beneficial to the retention and growth of slow-proliferating microorganisms, and the system's nitrification efficiency is improved. Can prolong the hydraulic retention time of some non-degradable organics in the system, which is beneficial to improve the degradation efficiency of non-degradable organics

Scope of application

It is suitable for small-scale hospital sewage treatment projects under 300 beds, especially for the small floor area and high water quality requirements.