On the sustainability of land applications of sewage sludge: How to apply the sewage biosolid in order to improve soil fertility and increase crop yield?

Evaluating the effectiveness of sulfidated nano zerovalent iron and sludge co-application for reducing metal mobility in contaminated soil

Sewage sludge has long been applied to soils as a fertilizer yet may be enriched with leachable metal(loid)s and other pollutants. Sulfidated nanoscale zerovalent iron (S-nZVI) has proven effective at metal sorption; however, risks associated with the use of engineered nanoparticles cannot be neglected. This study investigated the effects of the co-application of composted sewage sludge with S-nZVI for the stabilization of Cd, Pb, Fe, Zn. Five treatments (control, Fe grit, composted sludge, S-nZVI, composted sludge and S-nZVI), two leaching fluids; synthetic precipitation leaching procedure (SPLP) and toxicity characteristic leaching procedure (TCLP) fluid were used, samples were incubated at different time intervals of 1 week, 1, 3, and 6 months. Fe grit proved most efficient in reducing the concentration of extractable metals in the batch experiment; the mixture of composted sludge and S-nZVI was the most effective in reducing the leachability of metals in the column systems, while S-nZVI was the most efficient for reducing about 80% of Zn concentration in soil solution. Thus, the combination of two amendments, S-nZVI incorporated with composted sewage sludge and Fe grit proved most effective at reducing metal leaching and possibly lowering the associated risks. Future work should investigate the longer-term efficiency of this combination.

Organic Materials Promote Rhododendron simsii Growth and Rhizosphere Soil Properties in a Lead-Zinc Mining Wasteland

The mining of metal minerals generates considerable mining wasteland areas, which are characterized by poor soil properties that hinder plant growth. In this study, a field plot experiment was carried out in the mining wasteland of the Lanping lead-zinc mine in Yunnan Province to study the effects of applying three organic materials-biochar (B), organic fertilizer (OF), and sludge (S)-at concentrations of 1% (mass fraction), on promoting the soil of mining wasteland and the growth of two plant varieties (Huolieniao and Yingshanhong). The results showed that the amount of available nutrients in the surface soil of a mining wasteland could be considerably increased by S and OF compared to the control check (CK). In the rhizosphere soils of two Rhododendron simsii varieties, the application of S increased the available phosphorus (P) content by 66.4% to 108.8% and the alkali-hydrolyzed nitrogen (N) content by 61.7% to 295.5%. However, the contents of available cadmium (Cd) and available lead (Pb) were reduced by 17.1% to 32.0% and 14.8% to 19.0%, respectively. Moreover, three organic materials increased the photosynthetic rate and biomass of two R. simsii varieties. Specifically, OF and S were found to significantly increase the biomass of R. simsii. Organic materials have direct impacts on the increased plant height and biomass of R. simsii. Additionally, organic materials indirectly contribute to the growth of R. simsii by reducing the content of available Cd and available Pb in rhizosphere soil while increasing the content of available nutrients according to the structural equation model (SEM). Overall, S can stabilize Cd and Pb, increase soil nutrient contents, and promote the growth of R. simsii effectively, and has great potential in the vegetation reconstruction of mining wasteland.

A review on the fate and effects of contaminants in biosolids applied on land: Hazards and government regulatory policies

The increase in world population growth and its resultant increase in industrial production to meet its need, have continued to raise the volume of wastewater received by treatment plant facilities. This has expectedly, led to an upsurge in the volume of sewage sludge and biosolids generated from wastewater treatment systems. Biosolids are best managed by application on land because of their agronomic benefits. However, this usage has been discovered to negatively affect humans and impact the environment due to the accumulation of minute concentrations of contaminants still present in the biosolid after treatment, hence the need for government regulations. This review article examined the fate and effects of pollutants, especially persistent organic pollutants (PoPs) of concern and emerging contaminants found in biosolids used for land applications, and also discussed government regulations on biosolid reuse from the perspectives of the two major regulations governing biosolid land application-the EU's Sludge Directive and USEPA's Part 503 Rule, in an attempt to draw attention to their outdated contents since enactment, as they do not currently meet the challenges of biosolid land application and thus, require a comprehensive update. Any update efforts should focus on USEPA's Part 503 Rule, which is less stringent on the allowable concentration of biosolid pollutants. Furthermore, an update should include specific regulations on new and emerging contaminants and persistent organic pollutants (PoPs) such as microplastics, pharmaceutical and personal care products (P&PCPs), surfactants, endocrine-disrupting chemicals, flame retardants, pathogens, and organic pollutants; further reduction of heavy metal standard limits, and consideration of soil phosphate-metal interactions to regulate biosolid agronomic loading rate. Future biosolid research should focus on the concentration of TCS, TCC, and emerging pharmaceuticals, as well as Microplastic transport in biosolid-amended soils, soil-plant transfer mechanism, and metabolism of PFAs in the soils; all of which will inform government policies on biosolid application on land.

Comparative effectiveness of exogenous organic amendments on soil fertility, growth, photosynthesis and heavy metal accumulation in cereal crops

With soil fertility loss reached a critical state in arid and semi-arid regions, farmers are constrained to use mineral fertilizers, which are costly, non-eco-friendly and less effective in improving soil fertility than organic fertilizers such as dewatered sewage sludge (SS) and poultry manure (PM). In this regard, the current study aimed to highlight through experiments the positive effect of SS and PM applications on soil fertility and durum wheat growth. It targeted to demonstrate the safe and wise use of organic fertilization while assessing heavy metals in both soil and plant. The experiment was carried out in two batches of thirty-two pots, one for each treatment (SS and PM), in addition to the control with no fertilization. SS and PM were applied separately in three doses (D1 = 50 g, D2 = 100 g, and D3 = 200 g DM fertilizer/pot). The applications of both SS and PM induced a significant increase in plant-available phosphorus, organic matter, nitrates, moisture and electrical conductivity in soil, where these improvements were higher in PM compared to SS treatment. A significant accumulation of proline associated with an increase in biomass that were both proportional with fertilizer dose levels. Our findings revealed a loss in relative water content and leaf area of the plant. Correlations showed several significant relationships between soil parameters studied. The dose D2 of each fertilizer was the most efficient to improving both soil properties and plant components. Plant zinc concentration increased significantly with increase in soil zinc in PM amendments, however it decreased in SS. These relationships were not significant in copper for the two fertilizers. Both SS and PM improved soil fertility and plant growth compared to the control, thus this practice is a promising solution to tackle soil fertility loss and low production in drylands.

Yield, growth development and grain characteristics of seven Quinoa (Chenopodium quinoa Willd.) genotypes grown in open-field production systems under hot-arid climatic conditions

Quinoa is an important Andean crop that can play a strategic role in the development of degraded lands in hot arid regions due to its high nutritional value, genetic diversity and its high adaptability to stressful environments. The aim of this work was to evaluate the agronomic performance (growth development, grain yield and grain quality characteristics) of seven quinoa genotypes (Giza1, Sajama, Santa Maria, Q102, Q29, Q27 and Q18) cultivated under open field conditions in the Sahara Desert of Algeria. Using randomized complete block design (4 blocks), field trials were conducted during two cropping seasons (2017-2018 and 2018-2019) from November to April. The measured parameters included: plant height, number of panicles per plant, 1000-grain weight (TGW), grain yield (GYd), grain protein content (GPt), grain saponin content (GSC), and maturity indicators. The genotype effect was statistically the main source of variation in most parameters investigated as compared to the effect of cropping year. The Q102 genotype produced the highest GYd (2.87 t/ha) and GPt (16.7 g/100 g DM); and it required medium period (149 days) to reach harvest maturity as compared to other genotypes. The genotype Giza1 showed the lowest GYd and also low values for most of traits measured. However, it had the shortest harvest maturity (139 days) and the lowest GSC (0.62 g/100 g DM). The variety Santa Maria recorded the highest TGW (2.68 g), but it took 164 days to reach harvest maturity and it had high GSC (1.92 g/100 g DM). Though the best yield and grain quality characteristics were not reunited in single genotype, our findings showed that quinoa has multi-benefit potentials as a new crop for the arid agriculture in particular in hot-arid regions of North Africa.

Application of composted lipstatin fermentation residue as organic fertilizer: Temporal changes in soil characteristics and bacterial community

Lipstatin fermentation residue (LFR) is a byproduct of the pharmaceutical industry that may be disposed through land application after composting due to its high organic matter content. The effect of composted LFR application on the soil properties and microbial community still needs to be investigated before field application to verify its suitability and safety. Over a three months laboratory soil incubation experiment, the impacts of composted and raw LFR on soil properties, enzyme activities and bacterial community were investigated. The results indicated that the pH value of the soil fertilized with composted LFR decreased slightly, but the EC value increased significantly. It was worth noting that there was no measurable accumulation of lipstatin with LFR fertilization. The soil nutrients including available phosphorus, available potassium, organic matter and soluble organic matter were significantly increased in composted LFR-fertilized soil. In addition, the culturable microorganisms and enzymes were not inhibited throughout the incubation of composted LFR in soil. The composted LFR improved the soil fertility, environment and microbial biomass, which demonstrated its potential as a fertilizer. This study will provide a theoretical basis for the resource utilization of LFR.

A critical review on utilization of sewage sludge as environmental functional materials

Sewage sludge (SS) is increasingly used as an environment functional material to reduce or control pollution and improve plant growth because of the large amounts of carbon and essential plant nutrients in it. To achieve the best application results, it is essential to comprehensively review recent progress in SS utilization. This review aims to fill the gaps in knowledge by describing the properties of SS, and its usage as adsorbents, catalysts and fertilizers, and certain application mechanisms. Although SS generates several benefits for the environment and humans, many challenges still exist to limit the application, including the risks posed by potentially toxic substances (e.g., heavy metals) in SS. Therefore, future research directions are discussed and how to make SS applications more feasible in terms of technology and economy.

Integrating policy to achieve a harmonized sustainability model: A multidisciplinary synthesis and conceptual framework

While the concept of environmental sustainability has steadily grown over the past thirty years, little progress has been made in unifying the efforts of the entities most involved: society, the environment, the economy, and governmental policy. This synthesis integrates across disciplines to outline the need for a harmonized sustainability model to align disparate environmental objectives. Specifically, this study highlights the disconnect between policy and capitalistic economies regarding environmental sustainability. We then provide a framework for an updated sustainability model and offer pathways toward an improved state of environmental sustainability. Notable contributions include the development of a dynamic, harmonized sustainability model derived from basic supply and demand curves that functions for both the consumption and disposal of resources at multiple scales.

Treatment processes to eliminate potential environmental hazards and restore agronomic value of sewage sludge: A review

Land application of sewage sludge is increasingly used as an alternative to landfilling and incineration owing to a considerable content of carbon and essential plant nutrients in sewage sludge. However, the presence of chemical and biological contaminants in sewage sludge poses potential dangers; therefore, sewage sludge must be suitably treated before being applied to soils. The most common methods include anaerobic digestion, aerobic composting, lime stabilization, incineration, and pyrolysis. These methods aim at stabilizing sewage sludge, to eliminate its potential environmental pollution and restore its agronomic value. To achieve best results on land, a comprehensive understanding of the transformation of organic matter, nutrients, and contaminants during these sewage-sludge treatments is essential; however, this information is still lacking. This review aims to fill this knowledge gap by presenting various approaches to treat sewage sludge, transformation processes of some major nutrients and pollutants during treatment, and potential impacts on soils. Despite these treatments, overtime there are still some potential risks of land application of treated sewage sludge. Potentially toxic substances remain the main concern regarding the reuse of treated sewage sludge on land. Therefore, further treatment may be applied, and long-term field studies are warranted, to prevent possible adverse effects of treated sewage sludge on the ecosystem and human health and enable its land application.