**Background:** The world's population is projected to exceed 9.8 billion, requiring a 70% increase in food production. Conventional agriculture contributes to soil degradation, water overuse, and climate change. Hydroponics offers higher productivity in smaller areas with efficient resource use, but the most common method (NFT) requires high initial investment, limiting adoption by small family farmers. Substrate-based hydroponics using sand is proposed as a lower-cost alternative. This study aims to analyze the economic feasibility of implementing a sand-based hydroponic greenhouse for lettuce production on small rural properties in Dourados, Mato Grosso do Sul, Brazil.
**Methods:** The study was conducted at the rural worker union of Dourados/MS using primary data collected between January and March 2020. The greenhouse has an internal area of 390 m² with 18 benches (3.10 m × 1.80 m each), using treated eucalyptus structure, cement tiles, and sand substrate with drip irrigation. Production is 'Crespa Verônica Sakata' loose-leaf lettuce, with seedlings transplanted directly onto sandbanks and grown for an average of 42 days. Annual production capacity is 36,576 units. A 12-year project horizon was considered. The minimum attractiveness rate (MAR) was determined using the Adjusted Hybrid CAPM Model (AH-CAPM), yielding a MAR of 10.25%. Economic feasibility was assessed using net present value (NPV), internal rate of return (IRR), modified internal rate of return (MIRR), cost-benefit ratio (C/B), profitability index (PI), equivalent annual value (EAV), and discounted payback (DP). Sensitivity analysis and Monte Carlo simulation (100,000 iterations) were performed using triangular distributions for key variables: unit vegetable price, nutrient solution cost, pesticide cost, electricity cost, gasoline price, labor cost, and fixed investment.
**Key Results:** The initial investment required is $11,467.36 ($29.40 per m²), compared to approximately $36.22 per m² for NFT systems. Total annual costs are $6,213.25, with labor (24.91%) and variable taxes (16.15%) being the largest components. Gross annual revenue is $9,741.48 at $0.27 per unit. The economic viability indicators are: NPV = $15,575.63; IRR = 32.87%; MIRR = 18.14%; C/B ratio = 1.57 (net return of $0.57 per $1.00 invested); PI = 2.29; EAV = $2,314.00; discounted payback = 3.69 years. Sensitivity analysis shows that unit price accounts for 99.70% of NPV variability, while investment accounts for 0.2%, with a 95% confidence interval. Monte Carlo simulation at 95% confidence shows NPV between $252.13 and $30,213.25, confirming feasibility under risk conditions.
**Clinical Implications:** While not a clinical study, this research has public health relevance. Adoption of sand-based hydroponics by family farmers could reduce pesticide use—currently 86.8% of local family farmers use pesticides, which contaminate food, intoxicate workers, and pollute local rivers. The system promotes efficient water use, critical given that 40% of the world population faces water scarcity. Productivity is substantially higher: hydroponics yields approximately 313 tons of lettuce per year (31.3 tons per hectare, ten crops per year) versus 52 tons per year in conventional cultivation. The lower investment cost ($29.40/m² vs. $36.22/m² for NFT) and quicker payback (3.69 vs. 5.24 years) make this system more accessible to small farmers. Access to rural credit programs such as PRONAF in Brazil could further facilitate adoption. The study also suggests potential for integrating photovoltaic energy and rainwater harvesting to enhance sustainability.