Is it possible to maintain high salinity waste

The water cycle is an important part of the Controlled ecological life support system (CELSS), which includes the supply of drinking water and plant irrigation water, and the recycling of urine, sanitary waste water, and air condensate that water. Using urine and sanitary wastewater for plant culture is an effective way to reuse wastewater, but there are three main challenges. First, some salt content in wastewater especially sodium chloride is high, but it is not necessary for plant growth and may prevent plant growth. Second, wastewater contains organic substances such as surfactants, which also have a negative effect on plant growth. Third, if wastewater is used as the main source of nutrients, the proportion of mineral elements in wastewater may be inconsistent with the proportion of plant growth needs, which will also affect the normal growth of plants. In a research paper recently published in Space: Science & Technology, Liangchang Zhang confirmed the possibility of reusing treated wastewater (including sanitary wastewater and urine wastewater) as a hydroponic plant medium.

Two hydroponic media were used for hydroponic cultivation. One is the reused medium prepared to recover domestic wastewater from CELSS, and the other is the standard plant nutrient solution Hoagland nutrient solution. The composition of the two nutrient solutions is shown in Table 2. The used medium has a higher concentration of nitrogen (N) and potassium (K) and almost the same magnesium (Mg) and sulfur (S) concentrations.

Two types of crops, apium graveolens Linn (celery) and mesembryanthemum cordifolium LF (cordifolium) was selected in this study, which showed good salt tolerance in previous research. Celery was planted in box A and C, while cordifolium was planted in box B and D. For box A and B, the plants were cultivated using reused medium, and for box C and D, Hoagland nutrient solution was used.

As shown in Figure 1, celery cultivated in reused medium showed severe yellowing and wilting in the first 23 days; a concentrated liquor of micronutrient elements was added to the circulation tank of the corresponding cultivation box at 24^th day to improve the microelement concentration to the same level as the Hoagland medium. Then, the celery sprouted new green shoots at 32^n.d day, and the appearance was restored completely on the 43rd day. Like celery, cordifolium grown in reused medium shows a microelement shortage symptom that many leaves turn dark yellow green, and the cordifolium appearance returns to normal after supplementation with concentrated micronutrient liquor. The supplemental nutrient solution is shown in Table 3. Throughout the growing season, celery and cordifolium can be grown using recovery wastewater with micronutrient elements replenishment, in addition, cordifolium grown in reused medium shows better performance than the standard Hoagland nutrient. solution.

As shown in Figure 2, the pH of the reused medium, for celery and cordifolium, was lower than that of the Hoagland nutrient solution, that is, due to the relatively low initial pH of the recovery wastewater; on the other hand, there is a higher content of mineral elements (K, Na) in the recovery of wastewater, and plants absorb a large amount of cations and release H.⁺ , thereby reducing the nutrient solution pH. For both plants, the used medium has a faster increase in electrical conductivity than the Hoagland nutrient solution, indicating that the transpiration plants cultured with recovery wastewater is stronger than the plants cultured using Hoagland nutrient solution.

The concentration of macronutrient elements in all hydroponic media is shown in Figure 3. The difference in K content in the media for cordifolium is large, indicating a significant absorption of K⁺ and release of H⁺. The difference in NaCl in the media for cordifolium was higher than in the media for celery, which indicates that the cordifolium plant can absorb more NaCl in the used medium.

The concentration of micronutrient elements in four hydroponic media is shown in Figure 4. The B and Zn concentration can meet the requirements of normal plant growth throughout the experimental period. After adjusting the pH, the micronutrient concentration of Hoagland’s nutrient solution increased significantly, and the growth of cordifolium plants returned to normal (Figure 1). So, to maintain plant growth in Hoagland’s medium, it is necessary to prevent sedimentation by adjusting the pH.

The height of the plants (branch part) was recorded after harvesting as shown in Figure 5, and Table 5 the biomass weight of all the plants harvested in the experiment. Cordifolium plants produce more biomass than celery in one growing cycle. Therefore, it can be concluded that cordifolium is more adaptable to the used medium.

Figure 6 shows the weight of macronutrient elements and NaCl in shoot dry mass (SDM) and root dry mass (RDM). Both plants showed different NaCl absorption capacities, and the crop cordifolium had a higher performance than celery. Cordifolium cultivated in reused medium obtained the highest assimilation of NaCl. These results indicate that cordifolium has good stability and adaptability in salt-induced hydroponic environment. And celery can adapt to the used medium with high salinity but cannot absorb more NaCl.

references

Author: Liangchang Zhang , Yurong Xue, You Wang, Chengbo Zhan, Weidang Ai, Xingyan Wang

Original Paper Title: The Feasibility Research of Reuse of High Salinity Wastewater as a Plant Nutrient Medium for Plant Hydroponics at CELSS

Article Link: https://spj.sciencemag.org/journals/space/2022/9853421/

Journal: Space: Science & Technology

DOI: https://doi.org/10.34133/2022/9853421

Partner:

National Key Laboratory of Human Factors Engineering, China Astronaut Research and Training Center, Beijing 100094, China

Department of Environmental Science and Engineering, College of Environment and Resources, Xiangtan University, Xiangtan 411105, China

Space Institute of Southern China, Shenzhen 518117, China