The current sewage treatment problem has become a shortcoming that restricts green construction and development. Innovative research and development of construction technology for multimedia biofilters in sewage treatment plants. This technology has the characteristics of strong impact resistance, good treatment effect, high low temperature tolerance, ability to reuse reclaimed water, simple management and maintenance, low operating energy consumption and cost, no need for additional bacterial strains, small footprint, and good ecological landscape effect. Compared with similar technologies at home and abroad, it has obvious advantages in protecting water environment, intensively utilizing water resources, and saving operating costs.

Microbial detection plays an important role in food safety, environmental monitoring, and drug safety. The optical density (OD) detection method is the most commonly used method in the field of microbial concentration detection. In OD detection, aerobic bacteria require a large volume of oxygenated culture, which can lead to a higher OD of the bacterial solution. Therefore, how to expand the detection range is a key issue. To address the limitations of using operational amplifiers and lock-in amplifiers with limited dynamic range, a microbial OD detection circuit based on a logarithmic amplifier is proposed. The circuit uses the logarithmic amplifier AD8304 to meet the high dynamic range characteristics of OD detection. The theoretical calculation proves that this method can directly convert OD and output into a linear relationship, simplifying complex logarithmic calculations. To verify the feasibility of the scheme, an experimental device was built, and the linearity and stability of the circuit were verified by detecting the OD of standard OD tablets. In addition, the OD of three different concentrations of lactobacillus was detected simultaneously with a spectrophotometer, proving that the detection circuit can accurately detect the OD of microorganisms.