Analysis on the performance of vermifilter at low temperature in winter

Abstract

The performance of the vermifilter in winter was investigated. The experimental results indicated that the temperature of vermifilter bed in winter was 1~5 higher than that of the ambient. However, the temperature was still a key factor for the vermifilter, low temperature could influence the activity of the earthworms. The filter bed temperature was positively correlated with the earthworm density. So was the unit-area biomass. Reversely, the filter bed temperature was negatively correlated with the density of the mature earthworms. The results also showed that the earthworms' relative ingestion and digestion abilities were only about 1/3 of those in summer under the same hydraulic loading. Moreover, the removal rates of the pollutants except BOD 5 of the vermifilter effluent in winter was only half of that in summer under the same hydraulic loading. The average removal rates of TN and TP were both less than 10 %. Warmer area and better heat preservation medium are recommended to be provided for the vermifilter for its excellent operation performance.

Vermifiltration: Strategies and techniques to enhance the organic and nutrient removal performance from wastewater

“…Hence, to overcome the hindrance mentioned above to some extent and ensure the effective implementation of the VF technology, even in the colder climate, the researchers have adopted various innovative strategies to provide thermal insulation to the VFs, thereby protecting the micro‐environment inside the VF from the external freezing (Li et al, 2009; Yang et al, 2009; Yang et al, 2011; Yang & Zhao, 2008). For instance, Yang et al (2009) have introduced an elasticity plastic filler layer on the surface of the vermibed (schematically portrayed in Figure 2) to isolate the vermi‐ecosystem from the surroundings. The elasticity plastic filler layer acted as a barrier between the external environment and the vermibed media, eliminating their direct contact.…”

“…As a result, these earthworms get acclimatized very quickly to the wastewater treatment system, leading to the higher removal performance of the VFs (Binet et al, 1998) However, the application of this earthworm is beneficial only in the warmer climate since it flourishes at 15-25 C temperature . Furthermore, the studies indicated that the application of the E. fetida earthworms in colder regions resulted in a significant reduction in the nutrient and organic removal performance of the VFs (Arora & Kazmi, 2015;Yang et al, 2009).…”

“…Hence, this ensured that the VF temperature never dipped below 3°C—the earthworm's critical survival temperature, while treating the effluent from high load anaerobic biofilter. Yang et al (2009) found that, on average, VF ensured 21.75% and 46.78% removal of chemical oxygen demand (COD) and biological oxygen demand (BOD), respectively, during winter. In contrast, the same were 47.36% and 56.76% during summer.…”

“…Due to the appropriate use of elasticity plastic filler and ceramic pellets, the temperature inside the vermibed was always 1-5 C higher than the ambient temperature, even when the atmospheric temperature dropped to 2 C. Hence, this ensured that the VF temperature never dipped below 3 C-the earthworm's critical survival temperature, while treating the effluent from high load anaerobic biofilter. Yang et al (2009) found that, on average, VF ensured 21.75% and 46.78% removal of chemical oxygen demand (COD) and biological oxygen demand (BOD), respectively, during winter. In contrast, the same were 47.36% and 56.76% during summer.…”

“…Some of the commonly used bed materials in the VF process are peat and wood flour (Li et al, 2009); sawdust and vermicompost (Lourenço & Nunes, 2017a); woodchips, gravel, and quartz sand (Adugna et al, 2019;Li et al, 2008); riverbed materials, mud balls, and glass balls (Kumar et al, 2014); sand and vermicompost (Dey Chowdhury & Bhunia, 2021); ceramsite and coal (Wang, Yang, & Lou, 2010), and so on. Apart from providing the elasticity plastic filler layer, Yang et al (2009) have employed spherical ceramic pellets with 39.02% porosity, imparting high thermal insulation capacity, low specific heat capacity, and small thermal conductivity. Due to the appropriate use of elasticity plastic filler and ceramic pellets, the temperature inside the vermibed was always 1-5 C higher than the ambient temperature, even when the atmospheric temperature dropped to 2 C. Hence, this ensured that the VF temperature never dipped below 3 C-the earthworm's critical survival temperature, while treating the effluent from high load anaerobic biofilter.…”