Vertical hydroponic production of leafy vegetables with human-excreta-derived-materials (HEDMs) from decentralised sanitation technologies.

Abstract

Hydroponic production of leafy vegetables with human-excreta-derived-materials (HEDMs) extracted by decentralised sanitation technologies is projected to reduce food shortages while improving sanitation services in peri-urban communities, particularly in informal settlements. This study investigated the potential use of HEDMs generated by decentralised sanitation technologies for hydroponic production of leafy crops. HEDMs generated by decentralised sanitation technologies, namely: Anaerobic Baffled Reactor (ABR) and Nutrients, Water and Energy Generator (NEWgenerator) were used as treatments. A vertical hydroponic system called ZipGrow Farm Wall was assembled to conduct horticultural trials at Newlands Mashu Research site in Durban, South Africa. The vertical hydroponic system had eight vertical growing towers. Four vertical growing towers were fertigated with commercial hydroponic fertiliser mix (CHFM) as a control and the other four fertigated with HEDM as a treatment. A literature review was undertaken on open field and hydroponic production of crops with HEDMs. Previous and current studies indicated that nutrients derived from human-excreta have the potential to support the growth of plants even though low yields are obtained in some instance, and faecal pathogen contamination in crops occurs due to fertigation with infected nutrients. Only drip irrigation systems were reported to limit the transfer of faecal pathogens from nutrient source to plants. The first research study investigated the potential use of anaerobic baffled reactor (ABR) effluent on growth and yield of Swiss chard in a vertical hydroponic system. The results revealed that Swiss chard grown with CHFM performed better than those in ABR effluent and gave a significantly (p<0.05) higher plant height and fresh yield. Fresh leaf mass of Swiss chard was reduced in ABR effluent by 78 % when compared to CHFM. Sodium toxicity, ammonium toxicity, aphids and flea beetles reduced the growth and yield of Swiss chard grown with ABR effluent. Amaranthus in planted wetlands of ABR system hosted aphids and flea beetles who moved to defoliate matured Swiss chard leaves grown with ABR effluent as they thought it is a similar crop. In contrast, Swiss chard fertigated with CHFM suffered minimum effects of pest outbreak due to absence of faecal smell and nutrient stress. The second research study investigated the potential of diluted NEWgenerator permeate + hydroponic fertiliser (DNP + HF) on growth, and yield of hydroponically grown non-heading Chinese cabbage. The results revealed there was no significant difference in all determined growth parameters except for fresh yield (p>0.05) between plants fertigated by CHFM and DNP + HF. Fresh leaf mass of non-heading Chinese cabbage leaves was reduced in DNP + HF by 26 % when compared to CHFM. Significant yield decline in non-heading Chinese cabbage grown with DNP + HF was a result of nutrient conditions affecting the uptake and accumulation of nutrients in leaf tissues. Plant analysis revealed that uptake of macronutrients and micronutrient significantly varied in leaf tissues of non-heading Chinese cabbage between fertigation with CHFM and DNP + HF. Leaf tissues of non-heading Chinese cabbage showed higher levels of N, P, Mg, Mn, Na, Cu, Fe and Al while lower levels of K, Ca and Zn were observed when compared to plants grown with CHFM treatment. The deficiency and toxicity of nutrients in leaf tissues led to interference in photosystem activity of non-heading Chinese cabbage grown with DNP + HF which resulted on decline in final yield. On a positive note, harvested leaves were without faecal coliforms. These findings show that fertigation with ABR effluent and DNP + HF has the potential to support the growth of leafy vegetables in a hydroponic system. However, there is a need for further research to look at other aspects with negatively affected the final yield of crops.