Evaluating bioavailability of elements in municipal wastewater sludge (Biosolids) from three rural wastewater treatment plants in East Texas (USA) by a sequential extraction procedure

Evaluation and removal efficiencies of a rural WWTP for metals and anions in Lufkin, East Texas (USA)

The present study quantified element concentrations and evaluated the removal efficiencies of the Lufkin Wastewater Treatment Plant (LWWTP): a public municipal wastewater treatment plant in East Texas. Macroelements (Na, K, Mg, Ca, Al, Fe, Se, Zn, P, and S) and microelements (Ni, Pb, Mn, Cr, Mo, Cu, Co, V, As, B, Ba) were detected using ICP-OES and ICP-MS. In addition, the anion concentrations (Br^-, NO₃^-, NO₂^-, PO₄^3-, F^-, Cl^-, and SO₄^2-) and their percent removal from the LWWTP were assessed by using ion chromatography. Whereas macroelements in the influent were above the maximum ceiling limits, the total metal concentrations in the effluent were found below the USEPA (below μg/L) guidelines. In general, the removal efficiencies for metals in LWWTP were ≥ 94%. The removal efficiencies of the anions were > 100% (Br^-), 16.42% (Cl^-), 78.89% (F^-), 182.59% (NO₃^-), > 100% (NO₂^-), 51.81% (PO₄^3-), and 67.01% (SO₄^2-). In addition, Pierson correlation coefficients between the anions and cations, and implications for usage and suggested improvements of the treatment plants are proposed.

Evaluation and analysis of perlite and municipal wastewater sludge (biosolids) from three wastewater treatment plants in East Texas, USA

Municipal wastewater sludge (also known as biosolids) is produced in large quantities from wastewater treatment plants (WWTPs). Traditionally, analyses of biosolids revealed the presence of inorganic (including metals) and organic contaminants which pose health concerns to man and the environment. This study investigated physical-chemical parameters and comparative element concentrations (Ag, Al, As, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Mo, Ni, P, Pb, S, Se, Zn, V, Na, S, and P) in biosolids and composted wastewater sludge (CWS) from Nacogdoches Wastewater Treatment Plant (NWWTP), Lufkin Wastewater Treatment Plant (LWWTP), and Angelina-Neches Compost Facility (NCF) in East Texas (USA). In addition, concentrations in perlite, a hydroponic material, were determined via Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy/energy dispersive X-ray diffraction (SEM/EDX), inductively coupled plasma-optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD)), and thermogravimetric (TGA) analysis. Via ICP-OES analysis, metal concentrations in biosolid samples were similar. Macroelement amounts followed the order: NWWS ≈ LWWS > NCS > perlite. Notably, concentrations in biosolids, CWS, and perlite are below recommended USEPA and WHO maximum ceiling levels. The pH of biosolid samples was determined between 5.33 and 6.74. The weight loses of 6-19% wt at ~ 300-700 ℃ are attributed to volatile compounds and inorganic metal oxides. From environmental and circular economy perspectives, this study shows biosolids to be safe, and potential recycling can be encouraged for use in soil amendments. This finding could find impetus to design of much better WWTPs which improve removal efficiencies and encourage recycling of biosolids.