SUBSURFACE IRRIGATION COMBINED TO MEMBRANE DESALINATION FOR SUSTAINABLE USE OF BRACKISH WATER V. I. A. Lima 1; P. Le-Clech2; G. Leslie 3; B. G. Sutton 4
ABSTRACT: Two types of commercially available membrane, BW30 (RO) and FO8040 (FO) were tested during germination and seedling growth of common bean (Phaseolus vulgaris cv. Jade) for 15 days on tap water (0.3 dS/m) inside growth chambers. On day 16, membrane treatments were combined to two levels of evaporative demand (25oC-80% and 30oC-40%) and salinity (0.3 and 3.3 dS/m) giving a 3x2x2 completely randomized factorial design in triplicate. Membranes during germination were evaluated by first counting, germination percentage and coefficient of uniformity of germination. The comparison for seedling growth among treatments was performed by means of height, shoot and root length, dry mass for stem, leaves and root. For the final germination percentage, the FO was statistically equal to the control, and both 25% higher than the RO germination. For seedling growth, the RO presented higher values than the control and FO only for shoot elongation, 41 and 22%, respectively. Salinity was not found to have a significant effect on plant growth. Further trials of the FO membrane are expected to confirm the irrigation system’s validity and reliability to meet crops water demand when brackish water is available.
KEYWORDS: desalination, subsurface irrigation, water conservation
COMBINAÇÃO DE IRRIGAÇÃO SUBSUPERFICIAL E DESALINIZAÇÃO POR MEMBRANA PARA O USO SUSTENTÁVEL DE ÁGUA SALOBRA
1
PhD candidate, CAPES Foundation fellow, Brazil. UNESCO Centre for Membrane Science and Technology, School of Chemical Engineering, The University of New South Wales, Sydney 2052, Australia. Email:
[email protected] 2 Associate Professor, UNESCO Centre for Membrane Science and Technology, School of Chemical Engineering, UNSW, Sydney, Australia. 3 Professor and Director, UNESCO Centre for Membrane Science and Technology, School of Chemical Engineering, UNSW, Sydney, Australia. 4 Honorary Professor, Faculty of Agriculture and Environment at The University of Sydney and Visiting Professorial Fellow at UNSW, Sydney, Australia.
RESUMO: Dois tipos de membranas comercialmente disponíveis, BW30 (RO) and FO8040 (FO), foram testadas durante a germinação e crescimento de feijão comum (Phaseolus vulgaris cv. Jade) por 15 days irrigado com água de abastecimento (0.3 dS/m) dentro de câmeras de germinação. No décimo-sexto dia, tramentos com membranas foram combinados a dois níveis de taxa de evaporação (25oC-80% and 30oC-40%) e salinidade (0.3 and 3.3 dS/m) em um delineamento inteiramente casualizado em esquema fatorial 3x2x2 com três repetições. As membranas durante germinação foram avaliadas para primeira contagem, coeficiente de uniformidade de germinação e porcentagem de germinação (PG) . A comparação entre tratamentos para crescimento das mudas se deu pela altura, comprimento da parte áerea e raíz, e massa seca do caule, folhas e raíz. Para a PG, a membrana FO foi estatisticamente igual a testemunha, e ambas 25% superior a RO. Para o crescimento das mudas, a membrana RO apresentou maior altura que ambas testemunha e FO, 41 e 22%, respectivamente. Não se observou efeito significativo da salinidade nas variáveis de crescimento analisadas. Testes adicionais para a membrana FO confirmarão a validade e confiabilidade do sistema de irrigação em suprir a necessidade hídrica das culturas quando água salobra for disponível.
PALAVRAS-CHAVE: desalinização, irrigação subsuperficial, conservação de água
INTRODUCTION The water withdrawn by the agricultural sector was approximately 2,722 km3/year in 2007, which represented 69% of the global water consumption (FAO 2014), which is predicted to increase to 3200 km3/year by 2025 (UNEP 2008). Given this trend of increased demand, which for some localities exceeds the availability, the agricultural sector has been forced to consider sources of water other than fresh, such as desalination or wastewater reuse. An example of that reality is probably Spain, where more than 22% of the water produced by desalination is destined to agriculture (Zarzo et al. 2013); however, the production of irrigation water by conventional desalination requires complex and costly systems that reflects on the price of final production (Garcia et al. 2011). Many studies on the use of membranes have been reported to desalinate water for agriculture (Lotfi et al. 2015; Majeed et al. 2014; Bunani et al. 2015); however, water production from these systems is not directly driven by crop demand, which varies both diurnally and at different stages of plant growth, highlighting
the importance and need of a desalination method that couples water production to crop demand rate at reduced energy consumption. Based on that, a new concept of desalination for agriculture has been conceived: a subsurface irrigation method where irrigation pipes are fabricated from polymeric membrane material. Brackish water is used to feed the irrigation system pipes, which will be delivered directly to the soil-plant interface while limiting salts from reaching soil and plant, thus reducing damage of soil structure and yield decrease. This study was part of a series of experiments testing the irrigation performance for a range of membranes of varied configurations (Leslie & Sutton, 2009; Leslie et al., 2012; Lima et al. 2015; Lima et al. 2016b; Lima et al. 2016a), which aims to identify the best membrane configuration to achieve optimum efficiency of water delivery to crops based on their demand in quality, quantity and time. The study also covers the effect of evaporative demand and salinity level combined to membrane type during germination and seedling growth of common bean.
METHODOLOGY Two types of commercially available membrane, BW30 reverse osmosis (RO) membrane (Dow-Filmtec, USA) and FO8040 forward osmosis (FO) (CSM-Toray, Korea) were tested in triplicate during the germination of common bean (Phaseolus vulgaris cv. Jade, Sunland Seeds Pty Ltd, NSW) for controlled conditions of temperature (T) and relative humidity (RH) inside growth chambers. Seeds were germinated for membrane treatments according to similar methodology described in a previous study (Lima et al. 2016b). A control treatment was applied where no membrane was used and evapotranspiration was compensated for by difference in weight between consecutive days. Combinations of temperature and relative humidity were differentiated during germination, seedling establishment and post-establishment. Light inside the growth chambers was supplied by a combination of high pressure sodium (SHP) and incandescent lamps in a cycle with 12h daylight. From the start of the experiment, treatments were arranged in a factorial completely randomized design composed of three irrigation treatments (Direct, RO and FO-Toray) on tap water (0.3 dS/m); treatments were initially divided into two growth chambers at 25oC and 80% RH. Small T and RH variations between growth chambers were observed to affect evapotranspiration for the first day, after which all experimental tubes were re-joined inside one chamber up to the end of the establishment phase (15d). For that reason, the evaporative demand was considered in the statistical analysis as a covariate of change for
germination indexes and plant growth variables. After seedling establishment (day 16), tubes were differentiated into 12 treatments according to Table 1. Statistical analysis was performed using the software ASSISTAT (Silva & Azevedo 2006). Means were compared by Tukey test. Table 1. Treatment combinations of two combinations for temperature and relative humidity, two levels of salinity and three types of membrane Treatment 1 2 3 4 5 6 7 8 9 10 11 12
T and RH
Membrane type Control
Day: 25oC, 80% Night: 20oC, 80%
RO FO Control
Day: 30oC and 40% Night: 20oC, 80%
RO FO
Salinity 0.21 3.1 0.21 3.1 0.21 3.1 0.21 3.1 0.21 3.1 0.21 3.1
RESULTS AND DISCUSSION
Figure 1. Water balance for the RO and FO membrane, having the control as reference, for the duration of experiment
Figure 1 gives an overview of the water balance for the RO and FO membranes for the duration of the experiment, calculated as the water flux into soil for membrane treatments above or under the flux observed for the control. It can be observed that water transport for the RO membrane for the first 6 days was much lower than the FO. For day one, the FO membrane presented a water balance 11 fold higher than the RO, showing immediate spontaneous soil hydration in response to the high matric potential of the initially dry soil; while for the RO membrane, signs of wet soil surface started to appear only after the third day, however, remaining mostly dry for the duration of experiment (Figure 2).
Figure 2. Visual appraisal of soil wetting and germination for the control (a), FO (b) and RO membrane (c) at day 4
Figure 3 shows the effect of membrane type on first count of germination and coefficient of uniformity of germination (CUG). As previously reported, variation in T and RH was noticed between growth chambers for day one and taken into account in the ANOVA, which was found to have significantly affected both first count (p
