With the rapid development of charging batteries, electroplating processes, smelters, petrochemicals and other fields in China's modern engineering projects, the consumption of heavy metal elements such as lead, copper, nickel, cadmium, chromium, mercury, arsenic and other wastewater is gradually increasing, and the situation of heavy metal pollution in water quality is not optimistic.

The traditional treatment methods of heavy metal excess sewage, such as ion exchange, ion exchange, liquid biological fiber facial mask, electrolytic salt water and microbial adsorption, all have certain defects or deficiencies, such as expensive, difficult to control the reflection, unsatisfactory actual effect, difficult to recover and use precious metals, and very easy to cause secondary pollution. In recent years, the use of biological adsorbents to solve heavy metal pollution in wastewater has shown excellent practical results, with advantages such as: ① cheap and easily obtainable raw materials; ② Suitable wastewater with lower concentrations of heavy metals exceeding the standard; ③ Not easily causing secondary pollution; ④ Large adsorption capacity; ⑤ Excellent selectivity; ⑥ Some precious metals can be recycled and reused; ⑦ Wide application coverage. Most microbial adsorbents are floating microbial strains that appear in the form of microbial flocs, which are easy to disperse in the high-performance liquid phase. Therefore, the difficulty after adsorption is how to complete the solid-liquid separation equipment for adsorbents and substances.

Aerobic granular sludge adsorbent is a very typical microbial adsorbent, which not only has the advantages of general microbial adsorbents, but also has a unique biological structure type; The proportion of particulate matter is larger than that of water, and it has good precipitation characteristics, which can solve the problem of traditional microbial adsorbents being difficult to separate from water after adsorption.

1. The structural types of aerobic granular sludge

Aerobic granular sludge generally has a high packing density and maintains good sedimentation characteristics. It is a spherical pathogen with small particle size and high relative density, containing many extracellular polymeric substances (EPS). EPS contains many alcohols, end groups, hydroxyl groups, thiol groups, phenolic groups, etc. This functional group is very easy to react with heavy metal ions with different valence states in water quality, promoting the accumulation of a large number of metal ions on the surface of microbial strains. EPS has unique characteristics such as microbial strain structure, colloidal solution negative charge, and biological activity, which promote the capture of heavy metal elements in water quality. Therefore, aerobic granular sludge can be used as a natural heavy metal ion adsorbent to solve wastewater containing heavy metal ions.

2. Principle of aerobic granular sludge removal of excessive heavy metals

The removal principle of heavy metal elements by aerobic granular sludge is quite complex. At present, the analysis of domestic and foreign experts mainly relies on the use of simulation methods in the laboratory to conduct scientific research. The key is to study the individual behavior and reasons of aerobic granular sludge in removing wastewater containing a single heavy metal ion. There is relatively little scientific research on wastewater with different types of heavy metal ions coexisting. The key to the removal of heavy metal ions by aerobic granular sludge is based on extracellular polymeric adsorption, ion exchange method, metal material chelation, chemical precipitation, etc. HuiXu et al.'s research shows that the key to the removal of Ni2+from aerobic granular sludge is based on the entire process of ion exchange. At the same time, molecules such as O, N, S, and P contained in extracellular polymeric substances EPS and plant cell functional groups can chelate or complex with heavy metal ions, promoting the removal of heavy metal ions. Therefore, the organic chemical complexation of aerobic granular sludge cells and EPS on heavy metal ions is the main method for the adsorption of heavy metal ions by granular sludge.

HuiXu et al. proposed three principles of adsorption based on the technical aspects of X-ray diffraction, Fourier transform infrared spectroscopy analysis, and X-ray photoelectron device energy spectrometer: ion exchange method, EPS adsorption, and chemical precipitation. According to the results of natural environment scanner optical microscopy and X-ray energy spectrum analysis, Yao Lei et al. found that the entire adsorption process mainly consists of two processes: ion exchange adsorption and metal material chelation.

The process of removing heavy metal ions by microbial strains is generally a conclusion that various mechanisms work together. Heavy metal ions are likely to undergo redox reactions on the surface of bacteria and be removed, while some positive ions are likely to be removed due to sedimentation or evaporation. According to other methods, the removal of heavy metal ions is generally more primary and secondary, and the difficulty coefficient of testing in the experiment is relatively high. Further scientific research is needed to confirm the removal principle of aerobic granular sludge.

3. Factors affecting the removal of excessive heavy metals from aerobic granular sludge

(1) PH value.

PH value is the main factor that harms the removal of heavy metal ions from aerobic granular sludge, mainly by changing the concentration polarization characteristics of functional groups and the surface potential difference of sludge. HuiXu, YuLiu et al. found that the original pH value plays a key role in the removal rate of Ni2+by aerobic granular sludge and harms the zeta potential difference of aerobic granular sludge. Yang Xueyao et al. found that aerobic granular sludge has the best actual removal effect on Cd2+with a pH value of 6-7. Yao Lei et al. found that aerobic granular sludge has a strong practical effect on the removal of Pb2+at higher pH (5.0-6.0) standards.

(2) Touch duration.

The entire process of aerobic granular sludge adsorption of heavy metals exceeding the standard is generally divided into two stages: rapid adsorption and slow adsorption. Shen Xiangxin's research found that the equilibrium time for the removal of Cu2+, Cd2+, Zn2+, and Pb2+metal ions by aerobic granular sludge is about 2 hours; At the same time, scientific research on the actual removal effect of Pb2+shows that the entire process of aerobic granular sludge removal of Pb2+is a rapid adsorption behavior, and the adsorption amount in the first 5 minutes reaches 75.0% of the larger adsorption amount. Improving the understanding of aerobic granular sludge and heavy metal exceeding wastewater can improve the actual removal effect to a certain extent, but in practical project use, it represents the need to increase the capacity of the reactor, and further discussion is needed from the perspective of economic development effectiveness.

(3) Aerobic granular sludge particle size.

The particle size of aerobic granular sludge poses a significant threat to the actual removal effect. Both too high and too small adsorbent particle sizes are not conducive to the actual adsorption effect. The key to particle size is the specific surface area or reasonable total adsorption area of the adsorbent. Under the same conditions, generally small particle sludge has a large specific surface area, and the reasonable adsorption site level of its enterprise net weight adsorbent is higher, but at the same time, it directly affects the EPS composition of aerobic particle sludge.

(4) Environmental temperature.

The adsorption process of heavy metal ions by microbial strains and pathogens may be a chemical reaction or an exothermic reaction, which is greatly affected by the environmental temperature reflected in the management system. The environmental temperature is mainly based on factors such as the physical and metabolic theme activities of hazardous adsorbents, functional group adsorption thermokinetic models, and adsorption specific heat, thereby jeopardizing the actual adsorption effect. Shen Xiangxin's research shows that the adsorption capacity of aerobic granular sludge for heavy metal ions follows a whole process of first increasing and then decreasing with the increase of temperature. In the actual application of industrial wastewater treatment, increasing environmental temperature requires increasing heat supply, which incurs cost and may not be effective from an economic perspective. Usually, actual operation at room temperature is sufficient.

(5) The ion concentration of aerobic particulate matter (C0/X0).

The reasonable adsorption site level is a key parameter for demonstrating the vitality of aerobic granular sludge, which is related to the net weight of aerobic granular sludge and the concentration of heavy metal ions in the liquid. The adsorption capacity of aerobic granular sludge of enterprise quality is certain, so the ion concentration (Co/Xo) of aerobic particulate matter is the main factor determining its actual removal effect. LiuY, YangSF et al. found that the adsorption capacity of a certain quality of aerobic granular sludge for Zn2+is correlated with the original concentration value of zinc ions (C0) and particle concentration value (X0), and there is a certain linear correlation.

(6) Nutrients and metabolic phosphorylation.

The entire process of removing heavy metal ions by aerobic granular sludge microbial strains is a reflection of energy consumption. The appearance of nutrients in aqueous solutions is beneficial for promoting the theme activity of microbial metabolism, improving the actual removal effect, and at the same time causing certain metabolic phosphorylation. The valuable positive ions in nutrients and the phosphorylation formed by microbial metabolism are likely to compete with heavy metal ions in the market, posing a threat to the actual adsorption effect of aerobic granular sludge. There have been reports on the actual removal effects of microbial strains on heavy metal ions in glucose solutions with different concentration values. Norris's research found that microbial strains can increase their adsorption capacity for Cd2+and Co2+after adding 10mol of glucose solution.

(7) Coexisting positive ions.

The removal process of different heavy metal ions from aqueous solutions by microbial strains presents a competitive market effect, and the infectivity of different metal ions and aerobic granular sludge adsorption domains is different. Therefore, the presence of coexisting positive ions will inevitably harm the actual removal effect of aerobic granular sludge on the overall target positive ions. Jiang Meng's research found that when multiple metal material ions coexist, the actual removal effect of microbial strains on the overall target positive ions is somewhat reduced.

(8) Other influencing factors.

The removal of heavy metal ions from aerobic granular sludge is a comprehensive process with various reasons and overall effects. It is subject to various factors such as hydraulic power shear stress, hydrolysis acidification tank capacity, sludge age, and metabolic inhibition factors. At present, there are various cultivation methods for aerobic granular sludge, and the physical and chemical characteristics that immediately harm the sludge throughout the entire process, as well as the beneficial microbial species, are widely distributed. Different beneficial bacteria are a major factor that endangers its actual adsorption effect.

4. The development trend of aerobic particulate matter in solving heavy metal pollution in wastewater

(1) Research on the principles of complex substances.

The specific wastewater usually contains a variety of complex substances with various metal ions coexisting. Further research on the principle of removing heavy metals from aerobic granular sludge should be carried out, and the key is to conduct dynamic analysis and thermal analysis of the entire process, exploring the activation energy and entropy change during the adsorption process.

(2) Research on modified materials and retention methods.

The volume size and application convenience of absorbers are a major factor in their modern use. Exploring modified materials to improve the volume of aerobic granular sludge absorbers is a major direction, and finding a good way to retain aerobic granular sludge is a prerequisite for promoting industrial development.

(3) Analysis and active remediation research.

How to achieve the rational recovery and utilization of metal ions and the restoration of the activity of aerobic granular sludge after absorbing metal ions is a key aspect, especially the rational recovery and utilization of precious metals, promoting the reuse of biomass particles, and reducing secondary pollution.

(4) Research, development and design of processing technology equipment.

The fundamental purpose of using aerobic granular sludge to solve heavy metal pollution in wastewater is to achieve industrial application. It is necessary to integrate the characteristics of aerobic granular sludge itself, strengthen the development and design of production processes and reactors, and conduct research using specific wastewater to provide theoretical innovation and specific reference for modernization.

专业水处理的疑难问题，产品选型问题，可以单击下面的微信二维码电话联系贺工在线指导，长按微信二维码可自动识别添加贺工微信沟通解决您的疑难问题