## 3 Results and Discussion
### Effect of nWTRs on As Speciation in Biosolids-Amended Soil  
Table 3 shows the dominant chemical forms of As in the solution of soils with different treatments via the MINEQL+ modeling calculations that determine the soluble chemical As forms. The As speciation analysis showed that arsenous acid (H\({}_{3}\)AsO\({}_{3}\)) was the predominant chemical form (94.1%) in the control soil, followed by cacodylic acid [(CH\({}_{3}\))\({}_{2}\)AsO\({}_{2}\)H] of 1.3%, hydrogen arsenite (HAsO\({}_{3}\)\({}^{2-}\)) of 1.2%, arsenic trioxide (AsO\({}_{3}\)) of 1.1%, H\({}_{4}\)AsO\({}_{3}\)\({}^{+}\) of 1.1%, and di-hydrogen arsenite (H\({}_{2}\)AsO\({}_{3}\)\({}^{-}\)) of 1.1%. In the biosolids-amended soil the dominant chemical forms of As was arsenous acid (80%), followed by cacodylic acid of 9.7%, hydrogen arsenite of 2.2%, H\({}_{4}\)AsO\({}_{3}\)\({}^{+}\) of 2.2%, claudette (As\({}_{2}\)O\({}_{3}\)) of 1.4%, arsenolite (As\({}_{2}\)O\({}_{3}\)) of 1.4%, di-hydrogen arsenite of 1.3%, arsenic trioxide of 1.2%, and di-arsenic pentoxide (As\({}_{2}\)O\({}_{5}\)) of 0.6%. The application of nWTRs to the biosolids-amended soil significantly affected As speciation results, depending on the application rate of nWTRs (Table 3). The 0.25% nWTR treatment resulted in approximately 45% amorphous arsenic hydroxide or As (OH)\({}_{5}\) and 36% arsenous acid (As(III)) (Table 3), and also increased the proportions of cacodylic acid and di-arsenic pentoxide. However, with a higher level of nWTR treatment (0.5%), amorphous arsenic hydroxide increased to 56% but arsenous acid decreased to 19.6%. Cacoodylic acid and di-arsenic pentoxide also increased with increasing the level of nWTR treatment. The WTR application of 1% in the biosolids-amended soil increased the percentage of amorphous arsenic hydroxide, but arsenous acid percentage decreased (Table 3). Overall, the nWTR treatment was efficient in immobilizing As in the biosolids-amended soil. These research findings also support those reported previously by [PERSON] et al. [24] and [PERSON] et al. [40], showing reduced solubility of Cr and Hg in biosolids that were treated with Al\({}_{2}\)(SO\({}_{4}\))\({}^{3}\) or FeCl\({}_{3}\) compounds that are commonly used in drinking water treatment. Different As species have different physiochemical properties that determine their relative tendency to precipitate, adsorb, or dissolve in soil solution. Thus, evaluating nWTR effects on As speciation in agricultural soil is essential for developing the best environmental management practices with As-contaminated soil and water. [PERSON] et al. [41] reported that over 80% of As(V) and Zn(II) were steadily removed at solution pH 6 by the hybrid ion-exchange fabric/ceramic membrane system. Reduced flow rate and removal capacity were recovered through a backwashing process during continuous treatment with the hybrid ion-exchange fabric/ceramic membrane system. [PERSON] et al. [42], in their study about how arsenic lea \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**As Compounds**} & \multirow{2}{*}{**Control Soil**} & \multirow{2}{*}{**Biosolids (3\%)**} & \multicolumn{3}{c}{**nWTRs (\%)**} \\ \cline{3-5}  & & & **0.25** & **0.5** & **1** \\ \hline AsO\({}_{3}\)\({}^{3-}\) & 1.13 & 1.33 & 1.19 & 2.28 & 1.05 \\ HAsO\({}_{3}\)\({}^{2-}\) & 1.22 & 2.23 & 1.27 & 2.27 & 0.57 \\ H\({}_{3}\)AsO\({}_{3}\) & 94.11 & 80.02 & 36.04 & 19.59 & 13.98 \\ H\({}_{2}\)AsO\({}^{3+}\) & 1.09 & 1.33 & 1.45 & 1.14 & 1.06 \\ H\({}_{4}\)AsO\({}^{5+}\) & 1.12 & 2.2 & 1.21 & 1.57 & 1 \\ As(OH)\({}_{5}\) (amorphous) & & & 45 & 56.04 & 59.45 \\ Cacodylic Acid & 1.33 & 9.66 & 10.58 & 12.22 & 17.55 \\ Arsenolite (As\({}_{2}\)O\({}_{3}\)) & & 1.37 & 0.75 & 1.68 & 1.37 \\ Claudette (As\({}_{2}\)O\({}_{3}\)) & & 1.42 & 0.85 & 1.1 & 1.3 \\ di-arsenic pentoxide (As\({}_{2}\)O\({}_{5}\)) & & 0.55 & 1.66 & 2.11 & 2.67 \\ \hline \hline \end{tabular}
\end{table}