Due to the shortage of water resources in China, the state has implemented a series of rainwater harvesting projects. The safety of water quality cannot be guaranteed due to the lack of an effective construction, running, and management system. Slow filters are low-maintenance systems that do not require special equipment. In order to improve the performance of SSF in terms of the removal of bacteria and solid granules, e.g., the microorganisms attached to the surface of a single grain of the filtering material under a scanning electron microscope (50×) have been studied. Based on the improvements of conventional slow sand filtration (SSF), the bio-slow sand filtration method has effectively mitigated and helps to remove bacteria and other microbiological contaminants, as well as heavy metals, ammonia, nitrogen, organic material, and turbidity of the harvested rainwater. The removal efficiency of bioslow sand filtration was approximately 20-30% on particulate organic carbon, above 95% on ammonianitrogen, and better than 96%, 95%, 95%, 80%, 70%, and 60% on Cu2+, Cd2+, Fe2+, Zn2+, Mn2+, and Pb2+, respectively. The effluent quality meets the requirements of “standards for drinking water quality” in China. The result indicated the bio-slow sand filtration method could achieve better water quality results as an available water treatment technology.

The paper aims at providing a framework to calculate the agro-eco-compensation standard based on the systems agro-ecological concept of embodied energy as emergy. We have proposed a calculation system of eco-compensation standard for sustainable agricultural development based on the convertibility between emergy and price. According to our calculation, the total energy of agricultural production in Yongding River Basin was 3.45 E + 16 Sej/ha (the unit emergy value, expressed in solar emergy joules per unit) in terms of the renewable resources, nonrenewable resources, material inputs, and service costs. The energy of renewable and nonrenewable resources was 1.59 E + 16 and 1.86E + 16 Sej/ha, respectively. The ESI (environmental sustainability index) of the study area was 0.1056, indicating that its agricultural production was in a seriously unsustainable condition. To realize the sustainable agricultural production in the watershed, the downstream governments should pay $21.81 M (¥135 million) approximately to upstream governments for water and soil conservation. The results of the present study suggested that the emergy-based calculation method of agro-eco-compensation standard is feasible to a certain degree.

The nature-based solutions (NBS) concept is closely related to sustainability, harmonious and green development, resource rational exploitation, coupled human health and environment, and ecological protection priority. Bio-slow sand filtration (BSSF) technology is a green water treatment technology with low energy consumption, simple operation, and a high removal rate of contaminants. To achieve low cost, easy management and secondary pollution avoidance in the process of removing contaminants in drinking water, the rational selection of biofiltration materials and the optimal combination of particle size are particularly important based on NBS. To effectively remove turbidity, organic pollutants, bacteria, and ammonia nitrogen by BSSF, three scenarios were summarized by considering the influence of sensitive parameter optimization and the external environment (temperature and velocity). We designed three BSSF water treatment testing devices, which were filled with bio-filter materials with different particle sizes (0.15-0.3 mm, 0.3-0.9 mm, 0.9-1.35 mm, and 0.3-0.9 mm), to carry out an indoor testing comparison analysis. We optimized important parameters of BSSF water treatment technology (such as the bio-filter material particle size and filling heights, filtering velocity, and suitable temperature) to obtain the best design and operational parameters of BSSF water treatment technology. The optimum operating conditions were: filter material particle size of 0.3-0.6 mm, filling height of 0.6-0.9 m, filtering velocity of 0.2-0.6 m/h, and a suitable temperature of 15-35ºC. To ensure the water quality of the filtered water, we optimized the design parameters of traditional BSSF technology, which could save land and reduce beginning time. BSSF water treatment technology based on NBS is useful for promoting the engineering application of drinking water treatment and regional water security.