## 1 Introduction
### Research Gap  
Passive water treatment systems like the ones proposed by AC can be a sustainable and energy-independent solution for delivering safe drinking water, especially in rural and off-grid communities. Operation without pumps, by relying on gravitational force to move water through treatment stages, such as sedimentation, filtration, and disinfection, contributes to their simplicity and low maintenance requirements, making them particularly well-suited for remote and resource-constrained environments. Reported performance evaluations of full-scale passive plant, such as those implemented in rural Honduras based on the AC designs, indicate consistent removal of turbidity to levels below 1 NTU even during variable weather conditions, meeting WHO recommendations for safe drinking water in the distribution system [42]. Similar results were reported for a pilot-scale household rainwater system in Australia, where turbidity was reduced to 0.3-0.4 NTU using a gravity-driven membrane and granular activated carbon filter [43]. In another study, a gravity-fed membrane system using silver nanoparticle-coated microfilters successfully treated high-turbidity water (40-700 NTU), achieving a final turbidity <1 NTU, while also eliminating microbial contaminants [44]. These findings indicate that the passive systems, when well-designed and maintained, can achieve high levels of physical and microbiological water quality. However, their long-term success depends on factors such as source water variability, system operation, and protection against recontamination during storage or distribution.  
However, in the context of the AC technology, a key gap in the literature is the lack of controlled, long-term performance data for the operating systems. This study addresses that gap through the evaluation of PF200--a miniature, prefabricated water treatment plant based on AC design principles. Intended to serve a small community of approximately 200 people, PF200 offers a portable, low-cost platform for testing and optimization in a controlled setting. Figure 1 compares this pilot unit with a 10 L/s full-scale AC plant built in 2018. Figure 1 shows the comparison of a full-scale AC design of a 10 L/s plant created in 2018 and the tested pilot. For this study, PF200 was used as a representative pilot test platform. The goal of the experiments was to optimize the operation and evaluate the performance of a water treatment process in an AC plant. As a test rig, it has the advantages of being relatively low cost and portable, enabling its easy deployment in a controlled environment, which allows for better experiment monitoring than the full-scale implementations of the AC technology in Central America.  
The long-term success of the water treatment system depends not only on design but also on factors like source water variability, operational reliability in coagulant dosing, and post-treatment contamination risks. Furthermore, performance evaluations conducted by non-technical users may be prone to subjective biases and operational inconsistencies, limiting the accuracy of field assessments. The goal of this article is to conduct tests of PF200 in a controlled environment and to evaluate the performance of this setup against a full-scale conventional water treatment system built according to the United States Environmental Protection Agency (US EPA) design recommendations.