# Characteristics of Previous Concrete with Activated-Sludge Biological Fermentation
## 3 Results and Discussion
### COD Removal  
COD is a crucial indicator for evaluating the extent of organic pollutants in water bodies. Water with a high COD concentration has the potential to pollute water bodies, trigger eutrophication, impair water quality, and disrupt the balance of water ecosystems. Therefore, COD concentration serves as a reliable indicator of the degree of pollution in a water body. To accurately assess the COD removal efficacy of each formulation design, three samples were analyzed for each design. The average data from these samples were used as the results. The outcomes of the concrete samples subjected to the COD removal tests are presented in Figure 10. The results demonstrated that under identical conditions, the COD removal of the samples with AS addition was 29.5% higher than that of the samples without AS addition. Furthermore, under varying temperature conditions, the  
Figure 8: Fine analysis spectrum of C element of SPC at different curing temperatures. Figure 9: The content of carbon element substances in the sample. highest COD removal rate of 55.6% was observed for the sample at 30 \({}^{\circ}\)C, which was 4.5% and 16.7% higher than those of the samples at other temperature conditions, respectively. This phenomenon may be explained by the fact that the samples with added AS undergo microbial degradation reactions with organic matter during the hydration of the concrete, generating gasses that increase the number of micropores in the concrete. This improves the adsorption capacity of pollutants in the water. The elevated COD removal observed in the 30 \({}^{\circ}\)C sample may be attributed to the fact that this temperature is most conducive to microbial fermentation, which has a larger specific surface area and thus a greater pollutant adsorption capacity. This results in a higher COD removal. The results of this study indicate that maintaining the temperature at 30 \({}^{\circ}\)C may enhance the efficiency of COD removal. The persistent issue of elevated pollutant concentrations in the initial stormwater runoff presents a pressing challenge within the domain of environmental engineering. Multiple investigations have been conducted to devise innovative pervious concrete formulations with the aim of attenuating this environmental detriment. Although incremental advancements have been realized by modulating aggregate composition and granularity, alongside the application of photocatalytic titanium dioxide coatings, the enhancement in COD elimination rates remains moderate [30; 31; 32]. Subsequent inquiries have probed the incorporation of distinctive adsorptive materials into the concrete matrix to curb pollutant concentrations (as shown in Table 8). Despite the inherent sorptive potential of these additives, materials characterized by inferior adsorptive prowess have yielded unsatisfactory outcomes, even at escalated incorporation levels. Conversely, materials endowed with superior adsorptive quality have demonstrated removal efficiencies spanning 70% to 90%, notwithstanding modest admixture proportions. The present study diverges from preceding efforts by incorporating activated sludge as a novel admixture, exploiting the intrinsic microbial metabolic activities to bolster its adsorptive efficacy. Although this approach may not rival the efficacies of high-adsorptive materials, the utilization of activated sludge--an otherwise waste byproduct--affords substantial economic benefits. Beyond the cost implications, this approach may contribute to indirect reductions in carbon emissions and offer strategic alternatives for the comprehensive management of activated sludge. Figure 10: The capacity of concrete to remove COD in response to different curing temperatures. The addition of AS to concrete improved the COD removal efficiency, reaching a maximum value of 55.6% at 30 \({}^{\circ}\)C. This is due to improved microbial activity and microporous formation. Temperature optimizes the microbial fermentation process, increasing the specific surface area and the adsorption of pollutants.