Phosphorus removal process of sewage plant

Since the on-line monitoring of total phosphorus has been fully launched in domestic sewage plants, various sewage plants have experienced many stories, among which the most common is the chemical phosphorus removal process operation in sewage plants. This wave of operation has brought considerable troubles to the sewage plant in terms of technology, economy and management. Today, we will discuss the chemical phosphorus removal of the sewage plant.

Under the traditional biological phosphorus removal method, the total phosphorus in the municipal sewage plant is disturbed by sludge discharge and denitrification in winter, and can not maintain the stable operation effect of biological phosphorus removal. The chemical phosphorus removal process is adopted by a large number of sewage plants because of its simple operation, obvious phosphorus removal effect and high reliability of operation.

Because a large number of sewage plants use phosphorus removal agents for chemical phosphorus removal, it has set off a storm in the domestic phosphorus removal agent market. A large number of pharmaceutical manufacturers bring a wide range of phosphorus removal agents to sewage plants under the name of exclusive formulas, novel names and marketing means of various channels. The trend of the Chinese market has never been questioned. And are so many phosphorus removal agents under the banner of various high and new technologies really so unfathomable?

About the reaction mechanism of chemical phosphorus removal and the application of sewage treatment plant, you can click back to the series of phosphorus gate (top, middle and bottom). Today's article will not discuss this part. In terms of chemical principle, all phosphorus removal agents are inseparable from metal salts such as aluminum salt, iron salt and lime. Various famous phosphorus removal agents are nothing more than the different proportions of these agents. No matter what kind of phosphorus removal agent each sewage plant purchased, in fact, their effects are consistent in the end. Therefore, in the chemical phosphorus removal process, the selection of drugs is not the key point, but the attention to the biochemical system after dosing and the change of effluent quality is the key point of the process management of chemical phosphorus removal. This phase discusses the operation of chemical phosphorus removal in sewage plants.

The first problem of chemical phosphorus removal is the dosage. The traditional calculation formula is based on the chemical substances with clear content such as aluminum salt and iron salt. Now, in order to show their mysterious formula, various domestic agents are often unwilling to tell the sewage plant the specific components in the agents. As a result, the sewage treatment plant has to continuously adjust the dosing process until it is adjusted to the appropriate dosage. Moreover, for the sake of insurance, excessive dosing will be adopted in the dosing of the sewage plant. Excessive dosing will not only increase the cost, but also bring the superposition of chemicals in the system and the impact on the effluent. Especially for some medium and large sewage plants, this adjustment often takes several months, which consumes a lot of reagent costs, and the final result is still difficult to determine.

The reaction mechanism of chemical phosphorus removal will add chemical sludge to the water treatment system, which has been clearly shown in the actual operation of many sewage plants. Data at home and abroad show that in the process of chemical phosphorus removal, 20 ~ 30% more sludge will be produced than biological phosphorus removal, which will increase the operating pressure of sludge dewatering workshop. The sludge dewatering system of a considerable number of domestic sewage plants can not match with the sewage treatment system, and the normal biological sludge can not be removed from the system in a normal and timely manner. After adding this part of chemical sludge, the pressure of the sludge dewatering system is greatly increased. If there is no margin or the sludge dewatering system is not expanded and upgraded, the sludge of the system cannot be effectively dewatered and discharged. A large amount of sludge is accumulated in the sludge storage tank and part of it overflows back to the system. The phosphorus in the dephosphorized chemical sludge will be hydrolyzed again and return to the system, increasing the concentration of total phosphorus in the influent of the system, Thus, the chemical dephosphorization agent of the system is increased, and more chemical sludge is produced, which enters the sludge dewatering system and is released from the supernatant again, forming a vicious circle.

The impact of chemical phosphorus removal on effluent quality has also appeared many problems in the recent operation of chemical phosphorus removal process. Among them, the phosphorus removal agent using iron salt and its derivatives often needs to add excessive agent in order to ensure the effect of phosphorus removal. These excessive iron ions do not get sufficient reaction and eventually flow out of the sewage plant with the effluent. In addition, the advanced treatment units of some sewage plants are out of service or abandoned, and there are no measures to remove the excess iron ions and suspended solids in the effluent by precipitation and filtration, resulting in a high content of iron ions and suspended solids in the effluent. The high content of iron ions in the effluent will lead to the redness of the effluent quality, which is mainly due to the dyeing effect of Fe3 + in the water, resulting in the chromaticity exceeding the standard. A large amount of iron ions in the effluent will dye the areas flowing through, resulting in a bad sensory impression; And the suspended solids formed by containing phosphorus removal agents lead to the effluent quality SS exceeding the standard, etc.

The effect of adding chemical agents to the biological tank by synchronous method on activated sludge has been introduced in some domestic academic journals. According to the Research Report of Tsinghua University, the addition of chemical phosphorus removal Fe3 + and Al3 + has an inhibitory effect on the effect of activated sludge, in which Al3 + is stronger than Fe3 +. When the addition of Al3 + reaches 10-3mol / L, It will significantly inhibit the activity of microorganisms in the biochemical unit. However, it is also believed that this inhibition can be eliminated and balanced by biological sludge discharge and enhanced aeration. From the reaction of the chemical phosphorus removal process of the sewage plant at this stage, the aluminum salt of PAC, the known components (generally available in the market) and the mysterious phosphorus removal agent of the manufacturer have no obvious biological toxic reaction to the organism. However, this does not mean that there is no impact on biological reaction. At this stage, the sewage plant is under pressure from all aspects. Strengthening chemical dosing can ensure the standard of total phosphorus, which has become the main problem. However, there is no energy to take into account the impact on biological treatment, and there is no relevant technical personnel to make systematic organizational judgment, so the impact of this part cannot be evaluated. In fact, this also reflects the current operation status of domestic sewage plants at this stage. Taking the command of various external sticks as the main work goal, it has become secondary to truly and effectively develop the biological treatment capacity and ensure the good operation of biological nature.

The chemical sludge produced by chemical phosphorus removal enters the biological sludge in the sewage plant, increasing the amount of sludge by 20 ~ 30%. This part of sludge has changed the chemistry of the original biological sludge in the sewage plant. On the premise that the sludge of most sewage plants in China cannot be reasonably disposed of, this part of chemical sludge increases the difficulty of sludge disposal and causes new environmental problems. Similarly, sewage plants use a large number of chemicals to stimulate a large number of chemical industries to be put into production, and secondary problems to the environment will gradually appear in the future.

As the emerging chemical phosphorus removal problem of sewage plant in the past two years, the current stage is only the opening stage of the curtain, and a large number of subsequent problems will continue to emerge. As the operation and management personnel of sewage plant, they should recognize the problems behind chemical phosphorus removal, reduce the massive use of chemical agents through rational biological utilization, understand and strengthen the biological phosphorus removal effect, and treat nature in a natural way, so as to be accepted by nature. For the right and wrong of chemical phosphorus removal in the sewage plant, we also need to pay constant attention to and discuss. We welcome everyone to actively participate in and jointly face the phosphorus removal problem of the sewage plant.