Keywords

1 Introduction

Soil is a natural habitat of living organisms that contributes to basic needs like food and water. Soil accounts for sustaining the ecosystem & managing biodiversity to a great extent. It also acts as a vital resource that essentially contributes to the perseverance of life on Earth. Especially agricultural practices like food grain cultivation, horticulture & vegetation etc. solely dependent on the physicochemical properties of soil (Mishra et al. 2016). The inherent soil property has a direct influence on soil behaviour and nature; hence the comprehensive knowledge of soil properties, nature & behaviour becomes imperative managing environment in sustainable way (Sonwane et al. 2010).

Biotic & abiotic components of soil also have a role to play in soil health. Living components including plants, flora & fauna equally contribute to soil functioning. Soil acts as a major harbouring site for interactions where processes like decomposition, humification, solubilization & mineralization are taken place. These processes impact soil fertility by the reciprocal action of soil biota with humus materials, minerals and maintaining soil structure (Xue et al. 2021). Soil physicochemical characteristics such as pH, water content, availability of nutrients including the amount of carbon (C), nitrogen (N) and Potassium (K), etc. are very essential parameters. A slight imbalance causes a notable change in soil which directly or indirectly hinders its habitants. Therefore, soil quality necessarily has to maintain to confer its native functioning (Vincent et al. 2018).

In the last decade or so degradation of soil quality become a global issue of concern, where the soil is exceedingly contaminated by industrial effluents and solid wastes. Unplanned urbanization with booming industrialization, improper waste disposal, and anthropogenic activities had caused unsettling of soil composition & ended up with soil pollution. Industries without proper waste management systems are the biggest contributors to soil pollution (Lavanya et al. 2019; Kumar and Agrawal 2020). Industries like textiles, metallurgy, tannery, battery manufacturing industries, glass factories, microelectronics, paper processing plants, iron & steel plants, coal burning thermal plants, nuclear power stations, petroleum industries & plastics manufacturing etc. producing more pollutants which directly or indirectly released into the soil. The by-products of these industries are disposed of inappropriate manner as a form of effluent contains several organic and inorganic pollutants including toxic heavy metals and other non-biodegradable substances (Chhonkar et al. 2010; Zhan et al. 2015). The bioaccumulation of organic & inorganic waste materials & heavy metals in the environment exert toxicity & causing several health issues to the living world (Tchounwou et al. 2012; Jaishankar et al. 2014; Engwa et al. 2019; Zwolak et al. 2019). Especially heavy metals, pesticides & other xenobiotic compounds present in industrial effluents, are not biodegradable and have the tendency to persist in the environment, and their concentrations can be magnified significantly with time. These pollutants are not water-soluble thus they primarily accumulate on top layer of soil (Mishra et al. 2016). An elevated concentration of these could cause severe damage to the living cells by showing extreme toxicity due to inhibition of metabolic reactions (Vongdala et al. 2018). Plants’ lifecycles are shortened when they are exposed to such high contamination due to the inability to adapt that abrupt change in soil chemistry. Even the plant-associated microorganisms found in soil (Fungi and bacteria) begin to decline; their natural interactions disrupted which creates additional problems to the soil. It slowly hampers fertility and converts land unsuitable for agriculture and any vegetation to survive.

Urban & rural household waste materials also cause problems as they are been discharged in the environment in an uncontrolled manner. Sewages & garbages from domestic as well as commercial waste sources primarily consists of plastics, papers, discarded food, clothes, metallic cans, sludge, glasses, fibers, bottles, rubbers, etc. Among these, a few are biodegradable and are recycled by composting, while non-biodegradable materials are disposed of in landfills. Landfills are common in practice and economical but uncontrolled disposal of solid wastes gives rise to major consequences related to soil sustainability. It creates nuisance and has considerable environmental impacts by unsettling the soil ecosystem. These kinds of open landfills produce sanitary problems and act as a harbour of insect vectors & major sources of vector-borne pathogens. These waste dumps also produce several organic acids that percolate into the soil and cause underground water contamination (Chadar and Chadar 2017). Several reports suggested that the production of acids resulting in an acidic environment may inhibit biodegradation of waste materials by inherent microbial communities. In due course those soil ecosystems destroyed fully and are converted to the barren and unfertile land, unable to support any life on it.

Recent studies revealed that the presence of radioactive nuclei impacted soil degradation greatly, which is one of the pivotal factors of soil pollution generates both naturally and in a technogenic way. Emission of radioactive elements like 3C, 60Co, 90Sr, 137Cs, 226Ra, 232Th, 238U and 239Pu, etc. from nuclear power plants contaminate soil and accumulated in the vegetables and crops grown on that contaminated soil (Aleksakhin 2009; Ali et al. 2019).

Several bodies are formed in many countries in order to regulate and minimize the pollution level. Environmental Protection Agency (EPA) is one such organization working on the restoration of the environment by making a perfect balance of sustainability, economy & Society (report.epa.gov 2016). Published literature suggested that potential biological remediation strategies can be employed to retrieve soil native nature. Biological operations like microbial remediation or phytoremediation are effectively used for the removal of soil contaminants to a great extent. Especially microbial cells exert various processes including oxidative reduction, precipitation, mineralization, biosorption, complexation and enzymatic transformation by which hazardous pollutants are removed from soil efficiently (Ojuederie and Babalola 2017; Igiri et al. 2018).

The prime focus of this study is to recount the profuse sources & nature of soil contamination through industrial effluent and solid wastes & plausible soil restoration strategies (Fig. 20.1).

Fig. 20.1
A pie chart of composition of solid waste as per U S E P A 2016: Percentage data follows. Food and green 44; Glass 5; Metal 4; Other 14; Paper and cardboard 17; Plastic 12; Rubber and leather 2; Wood 2.

Composition of Solid waste as per USEPA 2016

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2 Nature, Composition & Characteristics of Industrial Effluent

Industries generally discharge wastewater in untreated form into the environment. Including India, worldwide wastewater generation from industries and production plants is common in practice. It has been reported by several researchers that, due to the shortage of requisite space or lack of proper disposal management system, a huge amount of toxic liquid is produced and enters into the open environment. Most industries disposed of their raw effluents in nearby water channels, drains or open soil (Ahmed et al. 2016). According to the published data of CPCB in the year 2010, 13,500 million litre industrial wastewater produced per day in India. These effluents typically consist of organic & inorganic materials which exert high toxicity (Table 20.1). Organic pollutants mainly includes phenolic compounds, hydrocarbons, pesticides, azo dyes, esters, etc. (Bhargava & Saxena 2020). Heavy metals are major constituent of inorganic pollutants. Commonly found heavy metals in industrial effluents are arsenic (As), nickel (Ni), chromium (Cr), lead (Pb), mercury (Hg), and cadmium (Cd), etc. Certain free living electrolytes (K+, Ag2+, Na2+, Mg2+, Ca2+, Cl−, CO3−, HCO3−, Cl−) are also likely to be found in the form of inorganic pollutants (Subramani et al. 2014; Ahmed et al. 2016; Tejaswi et al. 2017) (Table 20.2).

Table 20.1 Different types of industrial effluent and their characteristics
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Table 20.2 Different organic contaminants in industrial waste water with their sources & functions
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The composition & chemical nature of the effluents varies according to the industries it released. Generally, industries like paper mills & Zn smelter release acidic (pH 3 to 5) drain water while the textile wastewater is alkaline in nature. On the other hand, oil refineries, paper sugar mills, distillery and effluents possess much higher organic carbon. These effluents also contain xenobiotic compounds like aromatic hydrocarbons, metalloproteins and phenol compounds (Ahmed et al. 2016).

BOD and COD are the crucial parameters used to determine the wastewater characteristics. Several reports suggested that the abnormalities in BOD & COD values (Chhonkar et al. 2010) of untreated industrial effluents are very high contributed by various organic acids (Table 20.3).

Table 20.3 Types of inorganic contaminants in industrial effluent with their sources & functions
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3 Sources, Composition & Nature of Solid Wastes

Generation of waste material is an unavoidable phenomenon where a huge amount of waste is produced through industrial processes, from manufacturing units, or in the form of municipal and urban garbage. But the problem arises when these toxic & hazardous solid wastes are disposed of in an open environment without any proper treatments (Agarwal 2016; Kumar and Agrawal (2020)). These untreated solid wastes cause several complications. Generally, developing countries do have problems with waste management where solid waste materials are dumped in a specific site or they can be used as landfill materials. Lack of space near-source stations is a major reason for that (Lavanya et al. 2019). Preferably waste materials are transported to outskirts areas of cities where landfills or dumpsites are located. According to Shankar and Shikha, in India, it is only about 40% of total municipal solid wastes are collected and dumped in specified sites in daily basis. Insufficient infrastructure adding up more problems and ended up with Piling up of hazardous materials (abdel-Shafy and Mona Mansour 2018; Ferronato and Torretta 2019) (Table 20.4).

Table 20.4 Type of solid wastes and their characteristics
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A massive amount of waste materials emancipate openly from industries can be categorized as hazardous and non-hazardous. Waste materials like papers, plastics, wood, cardboard, packaging materials are relatively less harmful and can be utilized further or recycled. However trashes of heavy industries like coal ash from thermal power plants, steel melting slag, scrap metal & blast furnace slag from the steel manufacturing unit, lime from pulp and paper industries, gypsum from allied industries, red mud and tailings other than Iron (e.g. aluminium, zinc and copper) from metal industries are really creates environmental problems (Agarwal 2016; Lavanya et al. 2019).

4 Impact of Industrial Effluent & Solid Waste on Soil Health

The solid & liquid industrial waste are rich in chemicals, which are non-biodegradable and exert toxicity. At elevated concentrations of these ingredients of wastes exert an adverse impact on soil health. The components present in effluents tend to change the chemical makeup of the soil. Overabundance may influence soil stability by altering composition and physical factors like pH, salinity, etc. Deposition of organic and inorganic materials into the soil also amend the microenvironment of soil which indeed very essential for crop production. Several instances proved that the precipitation of fly ash on topsoil nearby industrial belts result in the loss of fertility. The immediate consequence of that is the production of barren lands (Bhat 2015).

It is evident that bioaccumulation of heavy metals have shown phytotoxicity (Hiroki 1992; Ahmed et al. 2016). Many researchers have highlighted the lethal effect of heavy metals on biological systems. The physiology of cell interior (organelles) markedly affected by these toxic ions (Jayashankar et al. 2014; Brifa et al. 2020; Tarekegn et al. 2020). In general, metals are indispensable for plant growth. Physiological & biological processes are highly dependent on metal concentration with in the cell. Depending upon the dose and exposure these chemicals started affecting plant health & disintegrate soil natural microbiota functioning. The presence of contaminants like inorganic metals affect adversely & causes various plant diseases such as high concentration of Cd result chlorosis, excess Cu produces oxidative stress etc. (Ahmed et al. 2016).

Man made organic chemicals such as halogenated organic pollutants (HOPs), polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), BTEX (benzene, toluene, ethylbenzene, and xylenes), nitro-aromatic compounds and organophosphorus compounds are found in soil in large quantity. Their high molecular weight and poor water solubility makes biologically unavailable and therefore, tend to persist in the environment. These organic chemicals are potentially mutagenic and carcinogenic, often accumulates in vegetables & fruits and cause a major threat to humans (Perelo 2010; Ali et al. 2019).

5 Reclamation of Soil by Microbial Remediation of Industrial Effluent & Solid Waste Contaminants

Microbial remediation is considered as effective techniques for removing soil pollutants. One of the key attribute of microorganism is the capacity to transform soil pollutants into harmless entity by exploring their wide metabolic range. Especially, fungi and bacteria able to produce variety of extracellular enzymes and low molecular weight organic acids that can somehow modify organic pollutants. (Rajendran et al. 2003). Therefore, in-situ & ex-situ treatment of pollutants proven as a cost-effective, eco-friendly & sustainable approach (Megharaj et al. 2011).

5.1 Microbial Remediation of Heavy Metals

Heavy metal pollutants can be partially or completely removed from soil by utilizing the metabolic activity of microbes. It is an entirely sustainable process i.e. no harm to the environment compare to other physical or chemical processes. Microbes are employed to remove, reduce, transform or completely remove the heavy metals from the soil. Several genes either present in the genome or plasmid are responsible for these physiochemical activities (Rajendran et al. 2003).

Efficient microorganisms including Bacillus sp., Arthrobactor sp. Pseudomonas sp., Staphylococcus sp. Streptomyces sp., Aspergillus sp., Rhizopus sp., Sacharomyces sp. Penicillium sp. etc. are widely distributed in soil and effectively remediate soil under natural conditions (Table 20.5).

Table 20.5 Microorganisms & respective metals they remediate
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Tabak et al. (2005) described different mechanisms of bioremediation by which soil microbes can minimize the effect of heavy metals including bioaccumulation, bioprecipatation, biosorption, transformation, immobilization & cometabolism etc. Under an intuitive environment, microbes adopt one of these techniques and make toxic metals biologically unavailable.

5.1.1 Biosorption

Biosorption or bioabsorption refers to the physical attachment of metals on the cell exterior by extra cellular polymeric substances (Tabak et al. 2005; Tarekegn et al. 2020). Biosorption is strictly dependent on physicochemical properties of the host cell. The ion absorbing efficacy is greatly vary upon composition of cell wall, temperature & pH of the surroundings, surface area for contact and metal gradient, exposure time, ionic strength as well as the chemical nature of the metal ions, etc. (Shamim 2018). Biosorption is a very common technique employed by many fungal, algal or bacterial species to defend themselves against cadmium, silver, lead, or nickel etc. (Tabak et al. 2005; Tarekegn et al. 2020). According to Shamim (2018), the accumulation of metal ions is not ATP dependent process rather the concentration of metals in the exterior, i.e. chemo osmotic pressure greatly influences the uptake capacity. The ionic nature of the membrane along with the gradient created on either side helps in specific and nonspecific metal sorption. Especially the presence of peptide chain linked repeated unit of NAG (N-acetyl glucosamine) & NAM (1,4-N-acetylmuramic acid) make bacteria more negative charge which attracts positively charged metallic ions (Shamim 2018) (Fig. 20.2).

Fig. 20.2
An illustration of interactions of metals and microbes: Microbia cell at the center leads above to: biosorption, metal-microbe interactions, and bioaccumulation; at sides to bioleaching and microbially-enhanced chemisorption of metals; below to: biotransformation, biodegradation of chelating agents, and biomineralisation.

Source Tabak et al. (2005)

Interactions of metals and microbes affecting Bioremediation.

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5.1.2 Bioaccumulation

Microorganisms can retain toxic heavy metals within their biomass in a physical manner. It is evident that microbial cells are able to uptake metals through the cell membrane due to several compounds released by the cell (Tabak et al. 2005; Banerjee et al. 2015). Several indigenous soil bacterial genera accumulates toxic metals such as Escherichia hermannii and Enterobacter cloacae showed resistance against Cd and Ni, Bacillus cereus & Citrobacter sp. uptake Pb and Cd, Thiobacillus ferrooxidans & Bacillus subtilis absorb Ag & Cr respectively. Similarly, Pseudomonas aeruginosa (U) & Micrococcus luteus (Sr) are also reported to show bioaccumulation. Certain fungal species efficiently deal with metals e.g. Saccharomyces cerevisiae act on U (Urenium), Rhizopus arrhizus act on Hg and Aspergillus niger on Th (Thorium) etc. (Juwarkar 2010).

5.1.3 Biotransformation

Microbiological transformations deals with the conversion of notorious pollutants (heavy metals) which can participate in the metabolic process. This technique is very useful to detoxify hazardous metals by reducing them enzymatically. Microorganisms takes up metals ions and then undergo various reactions such as oxidation, reduction, alkylation or methylation (Tabak et al. 2005). For example, Corynebacterium sp. shows biotransformation & reduce Chromium from its toxic form (Cr6+) to less toxic form(Cr3+) (Zhao et al. 2021). Similarly, Bacillus licheniformis cells can reduce of Pb2+ to Pb0 enzymatically (Jin et al. 2018).

5.1.4 Bioprecipitation

Various microbial activity may result in the precipitation or crystallization of metallic compounds which facilitate transformation of noxious metals into comparatively harmless one (Tarekegn et al. 2020). Eltarahony et al. (2020) reported that growing microbial cells secrete carbonate compounds which trap heavy metals causing precipitation. Such depositions of metals are greatly elevated when microorganisms tend to produce secondary metabolites. Previous researchers have shown that bio precipitation of Pb in a compound form (PbHPO4) that precipitates on the cell surface of by Citrobacter sp. & Bacillus sp (Peens et al. 2018).

5.1.5 Bioleaching of Metals

Bioleaching or biomining is the extraction of specific metal from mineral-rich natural compounds (ore) through microbial transformation. Bacteria like Acidophilus ferrooxidans & Thiobacillus sp. are capable to extract Cu, As, Hg, Pb, Fe, Ni etc. efficiently from mineral ore (Jerez 2017). Biomining widely used as a replacement of conventional chemical mining proved to be cost-effective & hazard-free. Several reports suggested that the microorganisms which are associated with bioleaching tend to have tolerance towards heavy metals. Since, this process produce certain organic acids like citric acid, gluconic acid & oxalic acid etc. which aids the mineralization of insoluble metal sulfides into soluble one.

5.1.6 Biomineralization

Biomineralization is the transformation process by which metallic compounds turns into crystalline precipitates. Microbial induced mineralization mainly based on cellular metabolism where metals are subjected to modify chemically and partially precipitates on the cell surface.

5.1.7 Cometabolism

Cometabolism is the process where degradation of one compound dependent on another compound (Hazen and Terry 2015). Usually, it is referred to as the simultaneous degradation of two compounds where the first substrate is fortuitously degraded by an enzyme which is the metabolic product of another compound (the secondary substrate). Typically, the microorganisms involved in it having no direct benefit from each other. Such co-metabolism strategies explored to cope with complex pollutants (Daniel et al. 2019; Zhao et al. 2021).

5.2 Remediation of Organic Pollutants

The major contaminants like Poly aromatic hydrocarbons (PAHs) and Polychlorinated biphenyls (PCBs) popularly known as Persistent Organic Pollutants (POPs) are found frequently and are considered as recalcitrant due to their high molecular weight & low water solubility (Mir and Gulfishan 2020). However, certain indigenous microorganisms have shown the potential to degrade these materials partially without hampering the native ecosystem and make these carcinogenic biologically unavailable (Perelo 2010; Megharaj et al. 2011; Mir and Gulfishan 2020) (Fig. 20.3).

Fig. 20.3
Flowchart of scheme of microbial biodegradation organic pollutants: Organic contaminants lead to volatilization, bioaccumulation, leaching, and sequestration; biodegradation processes lead to product of biodegradation and mineralization of C O 2 and H 2 O.

Adapted from Tabek et al. (2005)

Scheme of Microbial biodegradation of organic pollutants.

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Microbes mediated biodegradation of organic pollutants primarily occurs by anaerobic or aerobic metabolism and are mainly based on various processes including Monitored natural recovery (MNR), biostimulation & bioaugmentation & addition of compost material etc. (Kang 2014). Under controlled physical conditions microorganisms utilizing catabolic enzymes like oxygenase or dioxygenase to transform pollutants and ultimately the products of the microbial activity incorporated in the metabolic pathway (Perelo 2010). Bacterial species like Pseudomonas sp., Burkholderia sp., Methococcus sp., Bacillus sp. etc. were studied for their biodegradation capacity of PAHs, & PCBs (Kang 2014) (Fig. 20.4).

Fig. 20.4
Flowchart depicts microbial biodegradation pathways of P A Hs with chemical structures. P A H trifurcates: 1. bacteria to C is Dihydrodiol, Catechol to Hydroxymuconic semialdehyde above and cis Muconic Acid below; 2. white rot fungi to ring fission; 3. fungi to Arene oxide, to trans-Dihydrodiol above and phenol below to conjugation.

Adapted from Sayara and Sanchez

Microbial Biodegradation Pathways of PAHs.

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5.2.1 Monitored Natural Recovery (MNR)

Monitored natural recovery (MNR) is a sustainable process of remediating polluted sediments (Perelo 2010). A combined approach (biological & chemical) is adopted to treat contaminated site for a time span under close monitoring. MNR often employed indigenous factors which minimize the ecological and human health related risk significantly.

5.2.2 Biostimulation

Biostimulation is the moderation of the growth parameters of microorganisms to enhance the rate of the bioremediation process in soil. Various nutrients such as phosphorus, nitrogen, oxygen, or carbon supplemented as stimulants for microorganisms (Ratnakar et al. 2016; Goswami et al. 2018). Preferably under controlled environment addition of the stimulants improves potential growth affecting biomass & accelerates bioremediation. (Igiri et al. 2018).

5.2.3 Addition of Compost

Many researchers have reported that the addition of inoculum in compost form in contaminated soil has shown a significant response in terms of bioremediation. (Kästner and Miltner 2016). Compost bioremediation has proven to be effective procedure for minimizing the toxicity of many types of contaminants, especially chlorinated and non-chlorinated hydrocarbons. This process works in a precise manner as it treats specific contaminants at specific sites therefore it is often called to as “tailored” or “designed” compost (Ratnakar et al. 2016).

5.2.4 Bioaugmentation

Bioaugmentation is the incorporation of exogenous microorganisms or genetically modified strains to contaminated sites to get rid of pollution. The idea behind this is to speed up the biotransformation of the hazardous elements into less toxic substances under optimized conditions (Kastner and Miltner 2016). These transformed substances can be further utilized by other microbes and be incorporated into metabolism (Smitha et al. 2017). This process is effectively used where other bioremediation processes failed to show satisfactory results due to the lack of sufficient microbial populations or efficacy (Megharaj et al. 2011).

6 Conclusion & Future Aspects

Rapid industrial development and unimpeded urbanization in an unplanned manner are producing enormous wastes and continuous uncontrolled dumping of these wastes affects soil physicochemical properties and productivity. There is no doubt about the need for industrialization at this progressive era but conservation of natural resources also indispensable & equally important. Thus, proper management and safe removal of wastes can be ensured to diminish soil pollution-related problems.