Experimental Study for Sand Filter Backwash Water Management: Low-Cost Treatment for Recycling and Residual Sludge Utilization for Radium Removal

Management of backwash water (BW) generated from sand filtration of groundwater naturally contaminated with iron (Fe), manganese (Mn), and radium (Ra) remains a challenge worldwide. The present study investigated the effectiveness of a low-cost clay ceramic filter for BW recycling along with residual sludge utilization for Ra removal from BW. A 15 day continuous ceramic filtration process operated at a constant flux of 2000 L/m2/d (83 LMH) showed 99% removal of Fe, Mn, and turbidity. The treated BW was found suitable for recycling back to the sand filters. Subsequently, the residual sand filter backwash sludge (BS) was collected, characterized by scanning electron microscopy (SEM) and X-ray diffraction, and examined as a potential adsorbent to the Ra. Results showed that the sludge constituted heterogeneous basic elements, with higher percentages of iron and manganese oxides. The sludge can be classified as typical mesoporous and poorly crystalline minerals consisting primarily of quartz and Mn2O3. Over 60% of Ra from the initial 2.1 bq/L could be removed by sludge in 30 min at neutral pH. The adsorption kinetics of sludge described well by the pseudo-second order model and Ra adsorption on the sludge were mainly controlled by chemisorption rate-controlling steps, intraparticle diffusion, and external mass transfer processes. Treatment of BW by low-cost clay ceramic filters and the utilization the BS for Ra removal would be a sustainable sand filter BW management practice.

Generation of Bioelectricity from Organic Fruit Waste

This research proposes an alternative for companies and farmers through the production of electricity using microbial fuel cells (MFCs) using waste from export products. Nine MFCs were manufactured with zinc and copper electrodes; and as substrates, pineapple, potato and tomato pulp wastes were used in the anode chamber, and residual sludge in the cathode chamber. It was observed that the MFCs with pineapple substrate generated higher values of the electrical parameters, resulting in voltage and current values of 0.3484 ± 0.003 V and 27.88 ± 0.23 mA, respectively. It was also observed that the maximum power density was 0.967 ± 0.059 W/cm2 at a current density of 0.04777 A/cm2 for the same substrate. Acid pH values were observed in the three samples, while the conductivity reached its maximum value on day 23 (69.47 ± 0.91 mS/cm) which declined until the last day of monitoring; the turbidity values increased abruptly after day 22 until the last day where a value of 200.3 ± 2.52 UNT was observed for the pineapple substrate. The scanning electron microscopy for the pineapple substrate MFC electrodes shows the formation of a porous biofilm on the zinc and copper electrodes. These results show that a new form of electricity production has been achieved by generating high voltage and current values, using low-cost materials.

Evaluation of the performance of titanium and zirconium salts as coagulants in industrial wastewater treatment: pollutant removal, sludge production, and sludge characteristics

In this study, titanium tetrachloride (TiCl4), zirconium tetrachloride (ZrCl4), and zirconium oxychloride (ZrOCl2·8H2O) were evaluated using jar test experiments as coagulants and compared with traditional aluminum sulfate (Al2(SO4)3·18H2O) and ferric chloride (FeCl3) for industrial wastewater treatment. The effects of the initial pH of 4–10 and initial coagulant doses of 10–100 mg/L on chemical oxygen demand (COD) and total suspended solids (TSS) removal were investigated. The performances of the five coagulants were also assessed in terms of the settled sludge volume, the sludge volume index (SVI), and removal efficiencies of metals, color, and total phosphorus (TP) under optimum conditions. In addition, the contents of the residual sludge produced for all five tested coagulants under optimum conditions were determined. The results showed that the maximum removal efficiency of COD (69.33%) was achieved using 100 mg/L TiCl4 at pH 8. The maximum removal efficiency of TSS (98.32%) was achieved using 50 mg/L Al2(SO4)3·18H2O at both pH 8 and 10. The settled sludge volume and SVI generated by TiCl4 were lower than that for the other four tested coagulants. ZrCl4, ZrOCl2·8H2O, FeCl3, and Al2(SO4)3·18H2O resulted in 128.13, 92.39, 72.26, and 69.66 mL/g SVI, while that using TiCl4 was 48.84 mL/g. Ti- and Zr-based coagulants achieved better removal efficiencies of TP, Zn, and Cu than FeCl3 and Al(SO4)3·18H2O. The residual sludge from using Ti and Zr coagulants had a very high TP content. The results indicated that Ti- and Zr-based coagulants could be used as alternatives to traditional coagulants for industrial wastewater treatment.

Biofertilizer potential of digestates from small-scale biogas plants in the Cuban context

The residual sludge from anaerobic digestion known as digestate has been used as a valuable biofertilizer, but the effect of the substrate, the configuration of the reactor and the operating parameter changes the quality and amounts of nutrients in it. Therefore, it is necessary to know its potential characteristic of fertilizer to apply it correctly in crops of national interest. The aim of this work was to characterize the digestate generated from three biodigester technologies (fixed dome, floating drum and tubular) and three substrates: swine manure, cow manure, and co-digestion of swine and cow manure obtained in the province of Sancti Spíritus, Cuba, in terms of nutrient and matter content. For this purpose, stratified statistical sampling was carried out to ensure representative samples and descriptive statistical techniques were used to process the analyses. The digestate was divided into liquid and solid fractions according to the dry matter content (15%). The content of organic matter and ash represented around 50% for both fractions, which enhances its value as a soil conditioner. The nutrient content of both fractions showed good fertilizing properties, having a nutrient ratio (NH4+:PO43-:K+:SO42-:Mg2+:Ca2+) in the liquid (0.002:0.80:0.10:1.00:0.89:0.93) and solid (0.0003:0.96:0.002:1.00:0.52:0.50) fractions, that would contribute to the return nutrients to the soil. The quality of the liquid fraction as irrigation water was assessed as good, according to the relationship between the concentration of the nutrients (Ca, Mg, Na and K) and hardness. Further research is needed on the appropriate dosage for the different crops, and its contribution to sustainable agriculture in the Cuban context.

Effect of use residual sludge from watertreatment plants as a partial substitute forclay for refractory bricks production

The sludge generated from water treatment has been classified as a potential environmental pollutant. Because of its chemical composition similar to clay, was proposed to evaluate the effect of its incorporation as a partial substitute for traditional clay materials in the manufacture of aluminosilicate refractory bricks. The raw materials used were characterized by XRD and XRF; the prototypes designed were mixed, extruded, dried and firing at 1200°C, evaluating their linear shrinkage, apparent density, porosity, water absorption and mechanical and pyroscopic resistance (melting cone softening point). The results show the addition of 10% of sludges from industrial water treatment plant, contributedto elevate the softening point the clay that obtaining a refractory brick capable to supporting a temperature up to 1430 °C