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The maximum permissible limit of N, P and K for growth are 20, 30 and 50 ppm, respectively
(Kumar and Chauhan 2019).
WH’s ability to cope with difficult environmental conditions makes it desirable for the
remediation process. During the 1970s and 1980s, WH was generally used for wastewater treatment
as the plant roots are very useful for the absorption of nutrients. The nutrients absorbed by the plant
are stored for growth (Alves et al. 2003, Reddy et al. 1983, Reddy et al. 1987). It can absorb nitrogen
in two stages, first from the medium and another from the sediment. It can also remove P, K and
other organic pollutants, including heavy metals (Chua 1998). WH can control algal blooms and
water quality (Barry 1998). It removes a large number of pollutants, such as BOD, N, COD, P, DO,
heavy metals, etc. (Gupta et al. 2012, Rezania et al. 2015) from the water bodies.
The ability of WH to grow in heavily polluted water makes it favored among plants that use it
in the phytoremediation process (Mahalakshmi et al. 2019, Sarkar et al. 2017, Ebel et al. 2007, Roy
and Hänninen 1994). According to Malik (2007) and Smolyakov (2012) a medium sized WH plant
can proliferate/spread 2 million/hectares. WH grows in water, which is enriched with nutrients, but
fails to grow in saline coastal waters (Jafari 2010, Rezania et al. 2015). Based on dry weight, the
growth rate of WH is 0.04 – 0.08 kg dry weight/m2/d, while the rate based on the surface coverage
is, 1.012 – 1.077 m2d–1 (Gopal 1987, Rezania et al. 2015).
14.5 Industrial Lignocellulosic Wastewater
In recent times, lignocellulosic biomass or waste has gained popularity as a green and sustainable
alternative energy resource for producing second-generation biofuels and bio-based chemicals
(Menon and Rao 2012, Chandel et al. 2018). Lignocellulosic biomass comprises of cellulose,
hemicelluloses and lignin. In different industrial processes, the physical and chemical structure of
the lignocellulosic biomass is transformed to suit the requirements of the process (Zhao et al. 2012,
Kumar et al. 2017). The two major industries in India that produce a large amount of lignocellulosic
waste include paper and pulp and the textile industry. Apart from this, the dairy industry also
produces a vast amount of wastewater, which can be remediated by WH. Although there are other
lignocellulosic industries which produce large amounts of wastewater, like the sugar industries, oil
industries, rice and other food processing industries, this chapter focuses on paper and pulp, textiles
and dairy industries.
14.5.1 Paper and Pulp Industry
The paper and pulp industry (P&P) is one of the largest water-consuming industries, which requires
approximately 5–100 m3 of water to produce 1 ton of paper. The amount of water consumption
mainly depends on the type of substrate used, types of paper produced, and amount of water recycled.
In modern industries, the consumption of water is lesser for 1 ton of paper production (Nakamura
et al. 1997, Doble and Kumar 2005, Holik 2006, Nemerow 2007).
According to the World Bank Group report, P&P industries in Canada produce 20 100 m3 waste
water per 1 ton of air-dried pulp (The World Bank Group 1999). Poor water management in the
industry results in large water consumption as only a small amount of water is reused (Toczyłowska
Mamińska 2017). Conventional treatment methods like biological treatment eliminate the organic
components from the water. On the contrary, biological decomposition is insufficient to reduce the
refractory organics like COD and other pollutants load below the safe discharge limit (Sevimli 2005).
To meet the recent environmental standards and limit water use, the conventional P&P industries
are forced to switch to sophisticated technologies such as membrane separation, electrowinning,
electrocoagulation and bioreactors (Toczyłowska-Mamińska 2017). Untreated P&P industry
wastewater contains a brown color and persistent organics, which cause serious environmental issues
if the water is discharged into the lakes or rivers directly (Hao et al. 2000). Organic and inorganic
pollutants, including tannins, chloride compounds, adsorbable organic halides (AOX), COD, TS,