Reuse potential of knit fabric dyeing industry sludge As fertilizer

Abstract

Bangladesh is a land of agriculture where about 80% people are farmers. Due to infertility or poor fertility of land in many areas farmers suffer a lot. For the reason, there are a huge demand of fertilizers. The demand of using fertilizers is increasing day by day. It will be praiseworthy to find an alternative source of commercial fertilizer or soil amender.

There are more than 200 knit fabric dyeing industries in Bangladesh. These industries produce a huge amount of sludge that causes environmental pollution. In this study it was investigated to find out the reuse potential of knit fabric dyeing industry sludge as fertilizer.

In this study sludge samples were collected from two different type ETP distinctly Biological type ETP and Bio-chemical type ETP from two separate knit fabric dyeing industries located at Gazipur and Narayangonj in Bangladesh. The samples were collected twice from each type of ETP to conduct two sets analysis named SET1 and SET2. Samples were collected using grab sampling method. Only four samples (two from Biological type ETP and two from Biochemical type ETP ) were studied. Sludge samples were dried at 1050C for 24 hours in the laboratory. Various selected physical and chemical properties were investigated from the dried sludge sample after grinding. The investigation was carried out to find pH, water solubility, Nonmetals such as Carbon, Hydrogen, Nitrogen, Sulfur etc., Oxides such as Calcium oxide, Magnesium oxide etc., heavy metals such as Arsenic (As), Lead (Pb), Chromium (Cr), Nickel (Ni), Zinc(Zn), Cadmium (Cd), Copper (Cu), Mercury (Hg), Sodium (Na), Potassium (K), Calcium (Ca), Magnesium (Mg), Iron (Fe) and Zinc (Zn) from the analysis of sludge samples. Heavy metal analysis was done by using Atomic Absorption Spectrophotometer (AAS)(Shimadzu AA-6800). Aqua regia method was followed to prepare the solution. Then, solution was filtered through 0.45 μm pore size filter paper. The filtered sample was then analyzed using flame emission technique in Atomic Absorption Spectrophotometer (AAS) machine to determine the concentration of heavy metals - As, Pb, Cd, Cr, Ni, Cu, Hg, Na, K, Ca, Mg, Fe and Zn. Toxicity Characteristics Leaching Procedure (TCLP) test for the sludge sample was conducted to analyze the long term leaching potential of heavy metals using USEPA method 1311. Fertilizer characteristics and different type of fertilizers were studied. It was compared the fertilizer characteristics to sludge characteristics and growth of plantation in different sludge soil mixtures was observed.

It is observed that 14.67 - 24.94% C, 4.2 – 5.6% N, 1.68- 1.83% S, 0.45 – 0.59% P in the sludge of biological type ETP after anaerobic digestion and 3.24 – 23.50% C, 0.58 – 0.67% N, 0.34 – 0.54% S, 0.27 – 0.29% P in the sludge of biochemical type ETP after anaerobic digestion and little amount of other nutrients present.

The test results show that the heavy metals are As 0.138 – 0.82 mg/Kg, Cr 49.9 – 58.9 mg/Kg, Pb 29.0 – 36.8 mg/Kg, Hg 0.00 mg/Kg, Cd 0.00 – 0.50 mg/Kg, Ni 12.2 – 13.6 mg/Kg, Zn 695.1 – 886.6 mg/Kg, Cu 214.2 – 323.1 mg/Kg in the sludge of biological type ETP after anaerobic digestion and As 1.89 – 4.81 mg/Kg, Cr 11.60 – 16.2 mg/Kg, Pb 28.4 – 26.6 mg/Kg, Hg 0.00 mg/Kg, Cd 0.00 – 0.50 mg/Kg, Ni 4.6 – 5.2 mg/Kg, Zn 252.0 – 336.9 mg/Kg, Cu 40.0 – 61.7 mg/Kg in the sludge of biochemical type ETP after anaerobic digestion. According to Fertilizer Recommendation Guide – 2012 by Bangladesh Agricultural Research Council the heavy metals present in both sludge of biological type ETP and biochemical type ETP are within the allowable limits.

In TCLP tests the concentration of heavy metals are As 0.0135 – 0.0317 ppm, Cr 0.022 – 2.99 ppm, Pb 0.129 – 0.187 ppm, Hg 0.00 ppm, Cd 0.00 ppm, Ni 0.020 – 0.028 ppm, Fe 37.43 – 128.27 ppm, Mn 0.0 – 1.82 ppm in the sludge of biological type ETP after anaerobic digestion and As 0.0065 – 0.0114 ppm, Cr 0.0 – 0.029 ppm, Pb 0.166 – 0.227 ppm, Hg 0.00 ppm, Cd 0.00 ppm, Ni 0.011 – 0.020 ppm, Fe 1.23 – 6.08 ppm, Mn 0.0 – 1.62 ppm in the sludge of biochemical type ETP after anaerobic digestion.

TCLP test results of two sets of analysis show that heavy metals ( As, Cr, Pb, Hg, Cd, Ni, Fe, Mn) concentration are within the allowable limits according to Fertilizer Recommendation Guide – 2012 by Bangladesh Agricultural Research Council.

Two sets sludge sample test results show that knit fabric dyeing industry sludge can be used as fertilizer. It is necessary to fix the proper mixing ratio before using sludge as fertilizer. Mixing ratio depends on the soil characteristics. Sludge disposal volume will be reduced if it is used as fertilizer.