For all living organisms, nitrogen is an essential element, while being the most limiting in ecosystems and for crop production. Despite the significant contribution of synthetic fertilizers, nitrogen requirements for food production increase from year to year, while the overuse of agrochemicals compromise soil health and agricultural sustainability. One alternative to overcome this problem is biological nitrogen fixation (BNF). Indeed, more than 60% of the fixed N on Earth results from BNF. Therefore, optimizing BNF in agriculture is more and more urgent to help meet the demand of the food production needs for the growing world population. This optimization will require a good knowledge of the diversity of nitrogen-fixing microorganisms, the mechanisms of fixation, and the selection and formulation of efficient N-fixing microorganisms as biofertilizers. Good understanding of BNF process may allow the transfer of this ability to other non-fixing microorganisms or to non-leguminous plants with high added value. This minireview covers a brief history on BNF, cycle and mechanisms of nitrogen fixation, biofertilizers market value, and use of biofertilizers in agriculture. The minireview focuses particularly on some of the most effective microbial products marketed to date, their efficiency, and success-limiting in agriculture. It also highlights opportunities and difficulties of transferring nitrogen fixation capacity in cereals.

Liquid and solid olive oil mill waste was treated by composting in a mixture with the organic part of municipal solid waste and rock phosphate. The transformations that occurred during the process were evaluated by physical, chemical and spectroscopic analyses. After five months of composting, the final compost presented a C/N ratio under 20, an ratio under 1 and a pH around neutral. A high level of organic matter decomposition paralleled a notable abatement of phenols and lipids. The results show the effective dissolution of mineral elements during composting. This transformation was followed by Fourier transform infrared which showed a decrease in the absorption bands of aliphatic bonds (2925 and 2855 cm⁻¹) and carbonyls of carboxylic origin (1740 cm⁻¹). In addition to the increase in humic substances and the improvement of germination indices, the parameters studied confirm the stability and the maturity of the composts. The absence of phytotoxicity opens the way to agricultural spreading.

The physicochemical process of coagulation–flocculation was highly effective and economically suitable for leachate treatment. The leachate is characterized by a high chemical oxygen demand (COD), between 2,153 and 2,707 mg/L. The organic matter was not easily biodegradable (BOD5/COD: 0.2–0.135). Metal concentrations ranged between 0.1 and 4.2 mg/L for Cr, 0.005–0.04 mg/L for Cd, and 0.3–0.8 mg/L for Pb. The formation of sludge and its aptitude for decantation were measured. Several parameters were selected to check the purification of the landfill leachate, and these include turbidity, COD, metals, and sludge volume. Treatment with FeCl₃ proved to be effective at pH 6.5, and for Al₂(SO₄)₃ the optimal pH was 5.3. The results indicate that coagulation–flocculation by FeCl₃ and Al₂(SO₄)₃ is very effective in the reduction of turbidity, with abatement reaching 95 and 98%, respectively. For COD, removal by FeCl₃ and Al₂(SO₄)₃ reached 67 and 60%, respectively, at optimal concentrations of 18.5 mmol/L Fe³⁺ and 5.82 mmol/L Al³⁺. Aluminum sulfate produced less sludge than ferric chloride. The volume of sludge produced by FeCl₃ remained around 800 ml/L, while the volume of sludge produced by the aluminum sulfate was 230 ml/L.

Canna indica L. (CiL) was used here in phytoremediation of mining soils. Our work evaluated the effect of AMF (i) on the growth and (ii) on the uptake of heavy metals (HM). The tests were conducted in the greenhouse on mining substrates collected from the Kettara mine (Morocco). The mine soil was amended by different proportions of agricultural soil and compost and then inoculated with two isolates of AMF (IN1) and (IN2) of different origins. After six months of culture, the results show that on mining soils (100%) only AMF (IN2) was able to colonize the roots of CiL with a frequency of 40 ± 7% and an intensity of 6.5 ± 1.5%. Also, the lowest values of shoot and root dry biomass are obtained on these mining soils with respectively 0.30 g and 0.27 g. In contrast, the accumulation of HM was higher and reached more than 50% of that contained in the mining soils, the highest values with 138 mg kg⁻¹ Cu²⁺, Zn²⁺ 270 mg kg⁻¹ and 1.38 mg kg⁻¹ Cd was recorded. These results indicate that the colonization of CiL roots by AMF (IN2) could significantly improve its potential to be used in phytoremediation of polluted soil.