Recycling of domestic wastewater treated by vertical-flow wetlands for irrigating Chillies and Sweet Peppers

Due to water scarcity in many arid countries, there is considerable interest in recycling various wastewater streams such as treated urban wastewater for irrigation in the agricultural sector. The aim was therefore to assess if domestic wastewater treated by different wetlands can be successfully recycled to water commercially grown crops. The objectives were to assess variables and boundary conditions impacting on the growth of two different types of peppers fed by domestic wastewater pre-treated by diverse mature constructed treatment wetlands. The growth of both Sweet Pepper (California Wonder; cultivar of Capsicum annuum Linnaeus Grossum Group) and Chilli (De Cayenne; C. annuum (Linnaeus) Longum Group ‘De Cayenne’) fed with different treated and untreated wastewater types were assessed. A few plants suffered from either a shortage and/or excess of some nutrients and trace minerals. The overall growth development of Sweet Peppers was poor due to the high concentrations of nutrients and trace minerals. In contrast, Chilies did reasonably well, but the growth of foliage was excessive and the harvest was delayed. High yields were associated with tap water and an organic growth medium, and a wetland with a high aggregate size, leaving sufficient space for biomass. Low fruit numbers correlated well with inorganic growth media and irrigation water contaminated by hydrocarbons. Findings indicate that nutrient concentrations supplied to the Chillies by a combination of compost and treated waste water are usually too high to produce a good harvest. However, as the compost is depleted of nutrients after about eight months, the harvest increased for pots that received pre-treated wastewater. The project contributes to ecological sanitation understanding by closing the loop in the food and water chain. Findings will lead to a better understanding of the effects of different wetland treatment processes on the recycling potential of their outflow waters.