During the last decade, the growing load of sludge from textile industries, the top foreign exchange earning sector of Bangladesh, is a common nuisance to environmental system and community health. The present study was aimed to minimize the environmental impact from the disposal of Electrocoagulated Metal Hydroxide Sludge (EMHS) by using it as a partial substitute of clay in the manufacturing of construction material like building blocks (BBs). Different batches of normal and pressurized building blocks (NBBs and PBBs, resp.) were prepared using up to 50% EMHS with clay and then fired at a particular temperature. EMHS proportion in the mixture and firing temperature were two key factors determining the quality of BB. BB did not show any deformation or uneven surfaces at any of the examined firing temperature. At higher firing temperature and EMHS proportion, more weight loss and shrinkage of BB were noticed. Higher compressive strength and lower water adsorption were found at lower EMHS content and higher firing temperature. It was explored that NBB and PBB with 20 and 30% EMHS in clay, respectively, and fired at 1050 °C would be usable for nonloading applications; namely, ornamental bricks, decoration purposes, and fence of garden.
Degradation of environmental quality due to unrestricted and objectionable discharges of sludge from industrial unit is a common practice in developing countries like Bangladesh where little or no treatment of waste residue is carried out before disposals in landfill site haphazardly or openly. Although textile and dyeing sector is a vital part of economic development, speedy and unplanned progress may result in a wide impact on natural resources and human being living within the close vicinity of the sludge disposal locations [
Various steps have been taken by the Government of Bangladesh to monitor the effluent quality of industries. Therefore, the volumes of wastewater treated and the quantities of sludge generated are increasing. Hence, recycle, reuse, and conversion of waste materials into a reusable one is critically important for environmental protection and sustainable development of the society. Sludge contains a wide range of components including organic and inorganic matter; bacteria and viruses; oil and grease; nutrients such as nitrogen and phosphorus; toxic heavy and trace metals [
A potential long-term solution seems to be recycling of the EMHS sustainably and using it for beneficial purposes. Solidification is such a technique that stabilizes and solidifies components of waste materials. The solidified products can be disposed of to a secure landfill site or recycled and reused as construction materials, namely, bricks, concretes, roofing materials, tiles, building blocks (BBs), and so forth if meet the specific requirements [
The wet EMHS samples (
Geoengineering, elemental, thermal, and morphological/microstructural analysis of samples were carried out using British Standard 1377 [
In molding process of NBB, EMHS was mixed with soil up to 50% on weight basis in 10% increment. EMHS-free mixture was also made as a reference. Dry mixing was done first and then 10% aqueous solution of sodium silicate (Na2SiO3) was added to make homogeneous paste and bind the materials in the mixture well. Mixtures were then introduced into a series of BB molds of
Fired BB specimen underwent a series of test including weight loss on ignition, shrinkage on ignition, water adsorption, and compressive strength to determine their quality using following equations
Compressive strength of BB was determined using a hydraulic press (Fred S. Carver Inc, Wabash, IN, USA). The testing blocks were placed in the flat surface of the equipment and then load was applied. When fracture was observed in the blocks that loading pressure was taken and divided by four to get compressive strength in PSI. Then this unit was converted to kg/cm2, where 1 PSI equivalent to 7.03069 × 10−2 kg/cm2.
Basic geoengineering properties of EMHS and EMHS amended soil were given in Figure
Basic geoengineering properties of EMHS at different mixing ratios with soil.
Twenty-two elements were detected by EDXRF in EMHS where Fe was the dominant metal (about 83%). Overall statistics of elemental concentration was given in Table
Statistics of elemental concentration (mg/kg) of EMHS.
Element | Mean ± STD | Range |
---|---|---|
Fe |
|
902.6–941.1 |
Si |
|
39.4–68.8 |
Mg |
|
10–157 |
Ti |
|
0.48–0.67 |
K |
|
0.72–1.66 |
Ca |
|
5.3–6.2 |
Cu |
|
0.34–0.78 |
Ni |
|
0.12–0.24 |
Zn |
|
0.28–0.34 |
Mn |
|
0.23–0.98 |
Zr |
|
0.02–0.07 |
Ba |
|
0.05–0.2 |
Cr |
|
0.08–0.250 |
Cd |
|
0.01–0.018 |
V |
|
0.03–0.300 |
Hg |
|
0.05–0.068 |
Sr |
|
0.052–0.088 |
Nb |
|
0.02–0.035 |
Ga |
|
0–0.024 |
Cl |
|
0.0012–0.0032 |
Br |
|
0–0.08 |
S |
|
0.001–0.015 |
DTG-DTA-TG profile of EMHS.
SEM micrograph of EMHS at (a) 100
Initially, BBs were considered unsuitable if they developed cracks during drying and after firing at tested temperature; or if deformation in the shape or size was observed [
Higher percentage of EMHS mixed with soil and fired at higher temperature showed more weight loss of NBB and PBB (Figure
Weight loss on ignition of (a) NBB and (b) PBB at different EMHS percentages and firing temperatures.
A good quality brick exhibits shrinkage below 8% [
Shrinkage on ignition of (a) NBB and (b) PBB at different EMHS percentages and firing temperatures.
Relationship between weight loss and shrinkage on ignition of NBB at (a) 950°C, (c) 1000°C, and (e) 1050°C and PBB at (b) 1000°C and (d) 1050°C at different EMHS percentages.
Water adsorption is a crucial factor affecting the durability of various types of building materials. The less the water infiltrates into blocks, the more the durability of the blocks and resistance to the natural environment are exposed. The degrees of firmness and compaction of BB, as measured by their water adsorption characteristics, vary considerably depending on the type of clay and methods of production used. Therefore, the internal structure of the BB must be strong enough to avoid the intrusion of much water. Water adsorption of NBB was related to the percentage of EMHS in mixtures (Figure
Water adsorption of (a) NBB and (b) PBB at different EMHS percentages and firing temperatures.
Water adsorption occurred in two stages. The first stage is characterized by the linear behavior of gains of mass of water with time. This phenomenon related to the larger capillary pores. In the second stage, the gains of mass of water with time followed a nonlinear behavior and the flow of water in materials occurs in the smaller capillary pores [
All construction materials must resist stress and strength of a material indicated its ability to resist forces at failure. It was greatly dependent on the amount of EMHS in the BB and the firing temperature. It decreased with the increase of EMHS in the mixture but increased with the increase of firing temperature in case of NBB and PBB (Figure
Compressive strength of (a) NBB and (b) PBB at different EMHS percentages and firing temperatures.
There was a linear and statistically significant relationship among different properties of NBB with firing temperature and percentage of EMHS in mixtures (Table
|
||||||
---|---|---|---|---|---|---|
0% | 10% | 20% | 30% | 40% | 50% | |
Weight loss on ignition | 0.95 | 0.97 | 0.96 | 0.95 | 0.89 | 0.96 |
Shrinkage on ignition | 0.81 | 0.85 | 0.99 | 0.98 | 0.98 | 0.98 |
Compressive strength | 0.81 | 0.83 | 0.8 | 0.85 | 0.97 | 0.68 |
There are several mechanisms of solidification of heavy metals containing waste sludge [
The textile industry is treated as the flagship of Bangladesh for its contribution in top foreign exchange earning trade of the country. As the amount of sludge produced by wastewater or effluent treatment plant of such industries is increased, effective reuse and safe disposal of residue become a vital issue. Sludge accumulation is a burden to the industry and affects the environment adversely. Present study systematically investigated the reuse feasibility of EMHS from textile industry in the manufacturing of BB as a partial replacement of soil. To assess the quality weight loss on ignition, firing shrinkage, water adsorption, and compressive strength of the manufactured blocks were inspected. EMHS amount and firing temperature were two key factors determining the overall merits of products. Higher firing temperature and EMHS proportion in the mixture resulted in an increase in weight loss and shrinkage of BB. With the increasing firing temperature and less EMHS proportion, less water adsorption was observed. Compressive strength of BB increased with higher firing temperature and lower EMHS proportion. EMHS containing up to 20 and 30% for NBB and PBB, respectively, and fired at 1050°C produced good quality blocks and these blocks can be used for nonloading purposes. Therefore, EMHS seems to be reused feasibly in the manufacturing of building materials like BB.
This work was financially supported by the Ministry of Science, Information and Communication Technology, Peoples Republic of Bangladesh under the National Science, Information and Communication Technology (NSICT) Fellowship. The authors are grateful for the thoughtful comments of two anonymous reviewers.