Electrochemical treatment of industrial sulfidic spent caustic streams for sulfide removal and caustic recovery

Alkaline spent caustic streams (SCS) produced in the petrochemical and chemical manufacturing industry, contain high concentrations of reactive sulfide (HS-) and caustic soda (NaOH). Common treatment methods entail high operational costs while not recovering the possible resources that SCS contain. Here we studied the electrochemical treatment of SCS from a chemical manufacturing industry in an electrolysis cell, aiming at anodic HS- removal and cathodic NaOH, devoid of sulfide, recovery. Using a synthetic SCS we first evaluated the HS- oxidation product distribution over time, as well as the HS- removal and the NaOH recovery, as a function of current density. In a second step, we investigated the operational aspects of such treatment for the industrial SCS, under 300 A m(-2) fixed current density. In an electrolysis cell receiving 205 +/- 60 g S L-1 d(-1) HS- over 20 days of continuous operation, HS- was removed with a 38.0 +/- 7.7 % removal and similar to 80 % coulombic efficiency, with a concomitant recovery of a similar to 12 wt.% NaOH solution. The low cell voltage obtained (1.75 +/- 0.12 V), resulted in low energy requirements of 3.7 +/- 0.6 kW h kg(-1) S and 6.3 +/- 0.4 kW h kg(-1) NaOH and suggests techno-economic viability of this process

Electrobioremediation of oil spills

Annually, thousands of oil spills occur across the globe. As a result, petroleum substances and petrochemical compounds are widespread contaminants causing concern due to their toxicity and recalcitrance. Many remediation strategies have been developed using both physicochemical and biological approaches. Biological strategies are most benign, aiming to enhance microbial metabolic activities by supplying limiting inorganic nutrients, electron acceptors or donors, thus stimulating oxidation or reduction of contaminants. A key issue is controlling the supply of electron donors/acceptors. Bioelectrochemical systems (BES) have emerged, in which an electrical current serves as either electron donor or acceptor for oil spill bioremediation. BES are highly controllable and can possibly also serve as biosensors for real time monitoring of the degradation process. Despite being promising, multiple aspects need to be considered to make BES suitable for field applications including system design, electrode materials, operational parameters, mode of action and radius of influence. The microbiological processes, involved in bioelectrochemical contaminant degradation, are currently not fully understood, particularly in relation to electron transfer mechanisms. Especially in sulfate rich environments, the sulfur cycle appears pivotal during hydrocarbon oxidation. This review provides a comprehensive analysis of the research on bioelectrochemical remediation of oil spills and of the key parameters involved in the process

An activated sludge treatment plant for integrated removal of carbon, nitrogen and phosphorus

During the last decade more stringent effluent requirements concerning the nutrients effluent values have been imposed by legislation and social concern. This paper presents a pilot-scale activated sludge prototype system which combines the UCT concept and the step denitrification cascade for integrated removal of carbon, nitrogen and phosphorus. The experimental unit includes an anaerobic selector and stepwise feeding in subsequent anoxic and oxic vessels for removal of BOD5/COD, suspended solids, nitrogen, and phosphorus. Raw municipal wastewater with influent flow rates ranging between 48-120 L/d was fed to the unit at residence times of 7-18 h and specific BOD5 loading rates of 0.23-1.08 kg BOD5/(kg MLVSS-d). The results of a full year operation show high removal efficiencies of organic matter of about 88% as total COD and 92% removal for BOD5 complete nitrification (93-99% removal of ammonia-nitrogen), high removal of Total Kjeldahl Nitrogen ranging between 87 and 97% and total nitrogen removal through denitrification of 70%. Phosphorus removal is fair because of the intense fluctuations in the incoming phosphate concentration. Moreover, plant configuration provides operational conditions that suppress filamentous bacteria and favour growth of floc-formers, leads to high sludge settleability characteristics (SVI < 130 ml/g)

Development and implementation of microbial sensors for efficient process control in wastewater treatment plants

This paper demonstrates the functionality, laboratory testing and field application of a microbial sensor, which can be modified to monitor organic pollution extent, toxicity and over-(under)load of wastewaters both under anaerobic and aerobic conditions. Since nitrification is related to protons formation and the addition of alkaline is necessary for pH control, an aerobic biosensor monitoring Na2CO3 consumption was developed and practically implemented to control the nitrification process. As CO2 is the respiration product from aerobic degradation which can be correlated to the organic pollution extent, the previous biosensor was modified to monitor and measure the online toxicity and BOD/COD. Under anaerobic conditions, the online measurement of NaOH consumption and biogas production allowed the detection of toxicity incidents and over-(under)load in the influent. Such toximeters get in contact with the wastewater the earliest possible, providing sufficient time for protection of sensitive biological wastewater treatment processes and for the implementation of control and management strategies

Growth of filamentous bacteria in an enhanced biological phosphorus removal system

Activated sludge bulking caused by filamentous bacteria Eikelboom type 021 N and Thiothrix spp. is reported for the first time in a multistage pilot-scale wastewater treatment plant for enhanced biological phosphorus removal (EBPR). Both types of microorganisms grew gradually reaching their maximum cumulative length within a period of 2 months. For identification of the strains, in addition to physiological observations under the microscope, Gram staining, Neisser staining and sulfur storage test took place. Results confirmed that biological nutrient removal systems may also suffer from sludge bulking. Plant configuration, wastewater composition, removal efficiency and filaments' growth stages were examined in relation to the occurrence of the certain strains in an EBPR system