Decentralised wastewater treatment effluent fertigation: preliminary technical assessment

W Musazura,Ao Odindo,Eh Tesfamariam,Jc Hughes,Ca Buckley

doi:10.4314/wsa.v44i2.10

Abstract

The Decentralised Wastewater Treatment System (DEWATS) can provide a potential sanitation solution to residents living in informal settlements with the effluent produced being used on agricultural land. This paper reports on a first step to assess the technical viability of this concept. To do so a pilot DEWATS plant was connected to 83 houses in the eThekwini Municipality. An experiment was conducted in a randomised complete block design with 2 treatments (DEWATS effluent irrigation and tap water irrigation + fertiliser) and 3 blocks. Banana and taro crops were irrigated using an automated drip irrigation system. Data on the weather, crop growth, nitrogen and phosphorus uptake and soil chemical properties were collected. Irrigation with DEWATS effluent was comparable to tap water + fertiliser especially for banana growth and biomass production. Banana and taro required 3 514 mm of irrigation effluent. About 0.0117 ha·household−1 (23.3 m2·person−1) was found to be an adequate area for effluent reuse. Wet-weather storage requirements were calculated to be about 9.2 m3·household−1. DEWATS effluent, after passing through a horizontal flow wetland, was unable to meet banana and taro nitrogen and phosphorus requirements. Nutrient monitoring is required when using anaerobic filter effluent from a DEWATS for irrigating banana and taro.

Highlights

The provision of onsite sanitation to residents living in informal settlements of South Africa, where centralised wastewater treatment systems cannot be afforded (Ashipala and Armitage, 2011, Cross and Buckley, 2016), is one of the major aims of local governments in South Africa (Hoossein et al, 2014)
About 0.0117 ha·household−1 (23.3 m2·person−1) is needed under the conditions studied at Newlands-Mashu
Storage requirements needed during wet periods were calculated to be about 767 m3 (9.2 m3·household−1 or 1.9 m3·person−1)

Summary

INTRODUCTION

The provision of onsite sanitation to residents living in informal settlements of South Africa, where centralised wastewater treatment systems cannot be afforded (Ashipala and Armitage, 2011, Cross and Buckley, 2016), is one of the major aims of local governments in South Africa (Hoossein et al, 2014). Irrigation of crops with treated wastewater is important for recycling nutrients and is preferable to direct discharge into rivers (Mateo-Sagasta et al, 2013) This creates a system whereby soil acts as a medium for nutrient retention allowing subsequent uptake by crops (Bame et al, 2013). Planning for wastewater use in agriculture must consider various technical aspects such as the site’s physical characteristics, the effluent quality and quantity, land area required and storage requirements during wetter periods. Specific objectives were to (i) characterise the DEWATS effluent (after the AF and again after a HFCW); (ii) determine effects on the growth of banana and taro in an intercrop; (iii) assess the potential of DEWATS effluent as a source of N and P for a banana/taro intercrop (iv) calculate banana/taro irrigation requirements with special reference to the study site and (v) use the information to determine land requirements for irrigating banana/taro intercrop with DEWATS effluent as an aid for municipal land-use planning

MATERIALS AND METHODS

Findings

CONCLUSIONS