Evaluation of Titanium Tetrachloride (TiCl4) as an Alternative Coagulant and Characterization of Recovered TiO2

Titanium tetrachloride (TiCl4) as an alternative coagulant to remove organic matters and nutrients from the effluent of the secondary wastewater treatment was evaluated by comparison of removal efficiency of total phosphorous to Al- and Fe-based coagulants. Also, the surface characteristics, elemental contents, and crystallinity of the TiO2 produced from wastewater sludge flocculated with TiCl4 coagulant were investigated depending on the calcination temperatures. The more dosages of coagulants were injected, the greater concentrations of the cations (Al+3, Fe+3, Ti+4) and hydrogen ions (H+) resulted in the lower pH. Also, TiCl4 formed larger and heavier flocs than other coagulants and resulted in greater T-P removal efficiencies with reduced amounts of dosage. The phase change of anatase and rutile crystalline structures of TiO2 incinerated from wastewater sludges of TiCl4 coagulant was observed at relatively high calcination temperatures due to the existence of mixtures of organic matters, nutrients, and various impurities in the wastewater sludges of TiCl4 coagulant. Both C and P atoms were found to be mainly doped in/on TiO2 and the C and P atom originated from residual carbon of the settled organic matters and phosphorus nutrients present in effluents from sewage treatment plant, respectively. Therefore, 600–800 °C is the optimal calcination temperatures for TiO2 produced from TiCl4 coagulant flocculated with effluents from sewage treatment plant.

Chemical Selection for Flocculation of the Sludges Produced During Lime Neutralization of Acidic Spent Pickling Solutions and Rinse Water from Steel Pipe Mill

Acidic spent pickling solutions and rinse water are produced during steel pipe acid pickling. They are usually neutralised with lime in a neutralisation plant and pumped in the form of a wet sludge to a landfill. This is one of the main environmental issues of Russian steel mills. The implementation of sludge treatment units, including equipment for sludge polymer conditioning and dewatering, is an import consideration when seeking to reduce the impact of steel mills on human health and the environment. The researches results of polymer conditioning of the aggressive wastewater sludges by flocculants are reflected in the paper. Sludge samples were obtained from the neutralisation plant of an Ural’s steel pipe mill. Sludges of two types were investigated: the sludge which is formed in clarifiers during spent pickling solutions neutralization with lime and the sludge which is formed in clarifiers during rinse water neutralization with lime. During the work non-ionic, cationic, and anion flocculants Praestol® efficiency was estimated. The shortest time of water capillary suction from the flocculated sludge was accepted as efficiency criterion of flocculant processing. It was defined with use of the capillary suction timer Fann® and Whatman® 17 chromatographic paper. It is established that: non-ionic focculant Praestol® 2500 dose of 4–5 g/kg dry solids is effective for conditioning of the sludge produced during lime neutralization of acid spent pickling solutions; the anionic flocculant Praestol® 2540 dose of 1.5–2 g/kg dry solids is effective for conditioning of the sludge produced during lime neutralization of acid rinse water. The empirical response surfaces and the contour plots showing the relationship between capillary suction time and a dosage of flocculant and a charge density (% hydrolysis) of a flocculant were reveived. Keywords: steel pipe mill, acid pickling, wastewater, sludges, flocculants, capillary suction time

A Review of Pretreatment Methods to Enhance Solids Reduction during Anaerobic Digestion of Municipal Wastewater Sludges and the Resulting Digester Performance: Implications to Future Urban Biorefineries

The rapid increase in the population is expected to result in the approaching of design capacity for many US wastewater treatment plants (WWTPs) over the next decade. WWTPs treat both municipal and industrial wastewater influents, resulting in the production of biosolids after digestion. Biogas, a potential recovered alternative energy source, is also produced as an output from successful anaerobic digestion. More than 7M of dry tons/year of biosolids produced in the US are most often disposed in either landfills or land-applied (~80%). These options are becoming more challenging to implement due to increases in transportation costs and tipping fees, decreases in the availability of landfill/landfarm space, and most importantly, increased regulations. This situation is strongly encouraging WWTPs to find alternatives for the disposal of biosolids. Developing alternative management/disposal options for biosolids are evolving. One of the most attractive alternative option from a sustainability perspective are biorefineries (converts waste to commercial products), which are a fast-growing option given the push toward circular urban source economies (little to no waste generation). Anaerobic digestion has been widely applied in WWTPs to reduce the volume of activated sludge due to its low energy requirements, effective handling of fluctuations due to organic loading rate, relative flexibility with temperature and pH changes, and since biogas is produced that can be transformed into energy. Various pretreatment methods for waste sludges prior to digestion that have been studied to reduce solids production and increase the energetic content of the biogas are presented and discussed. Solids handling and management, which comprises ~60% of the operational cost of a WWTP, is estimated to save more than $100 M annually by achieving at least 20% reduction in the annual production of biosolids within the US. This review incorporates an assessment of various pretreatment methods to optimize the anaerobic digestion of waste sludges with a focus on maximizing both biosolids reduction and biogas quality.