# Methods for Obtaining Humus Substances: Advantages and Disadvantages
## 3 Results and Discussion
### Advantages and Disadvantages  
The work aimed to analyze three humus substances produced using different methods and obtained from various raw materials. HS(A) is characterized by good solubility and is rich in mineral substances suitable for the soil. This product's disadvantage is the high production cost and high commercial price. HS(B) is an ecological product obtained from brown coal. It contains about 35% (Figure 3) of simple aromatic compounds, hydrocarbons, and carbohydrates. It contains 70% of carbon in the ash-free mass. It is rich in minerals necessary for the soil. The disadvantage of this product is that it forms a gel, which is not practical in agricultural use. HS(C) is obtained from waste, digested sewage sludge. The disadvantage of this product is the significant content of aromatic compounds, hydrocarbons, and carbohydrates, 63% (Figure 4). IR studies (Figure 5, Table 3) confirm that these might be aldehydes, esters, ketones, alkenes, and other aromatic substances [39; 40; 41; 42]. In addition, studies [3] show that in wastewater treatment plants, humus substances are carriers of medical products, PAHs, hormones, pesticides, and other substances that threaten humans (chemicals of emerging concern) [45]. It is a new and already popular term in world science. Previous studies have shown that humic substances, due to their aliphatic-aromatic structure, are an excellent carrier of organic and mineral pollutants. They form soluble complexes with cations and organic substances. That is why they carry various pollutants out of WWTPs, which many authors have confirmed [46; 47; 48; 49; 50; 51; 52]. Therefore, HS(C) requires additional tests to check their toxicity and the possibility of using them in agriculture. However, they can be used for remediation or non-agricultural purposes. Additional tests were conducted to more thoroughly analyze the advantages and disadvantages of the tested HS. HS exhibit an affinity for hydrophobic and electropositive surfaces, as shown in [53]. Analysis of the results presented in Figure 6B shows that the HS(B) solution contains suspended brown coal particles, with a size of <580 nm. These particles have a negative zeta potential (Figure 6A) in the \(-31\) to \(-54\) mV range. The highest value of the negative potential is at neutral pH (\(-54\) mV). The absolute value of the potential decreases along with decreasing pH and increasing proton concentration. The surface is protonated and, at a pH of about 3.3, its value is around \(-32\) mV. In addition, increasing the concentration of OH ions contributes to a change in the zeta potential value to about \(-46\) mV at a pH around 10.6. The particle size is the biggest (580 nm) at a neutral pH, at which the electric double layer is hydrated and dispersed. With increasing proton concentration, the negative zeta potential decreases, the double layer is more compact, and at pH 3.3, the particle diameter is 520 nm. Similar dependencies are observed in the alkaline reaction. Figure 7 shows the image of the HS(B) solution with suspended particles of undissolved brown coal. The negative zeta potential (Figure 6A) of colloidal and quasi-colloidal particles (Figure 6B) dispersed in the solution and a large amount of multi-positive calcium, iron, magnesium, and aluminum ions contribute to coagulation and formation of a gel from the HS(B) solution. For the HS(B) solution, the reference level is the HS(A) solution. Therefore, the change in their turbidity depending on pH was examined for both solutions. The results of the tests presented in Table 4 indicate that the HS(A) solution is clear. For only pH < 1, turbidity values occur in the 0.57-1.08 NTU range. Hence, we should conclude that the HS(A) solution contains mainly fulvic acids. At pH < 1, humic acids precipitate, causing a slight increase in turbidity. On the other hand, the HS(B) solution is turbid in the entire tested range from 0.7 to 10.5 pH. Its turbidity is in the range of 21.5 to 40.7 NTU.