The efficiency of wastewater treatment practices can be significantly improved through the introduction of new microbial treatment technologies. In order to meet increasing stringent discharge standards, new applications and control strategies for the sustainable removal of ammonium from wastewater have to be implemented. Partial nitrification to nitrite was reported to be technically feasible and economically favorable, especially when the wastewater with high ammonium concentrations or low C/N ratios was treated. For successful implementation of the technology, the critical point is how to maintain the partial nitrification of ammonium to nitrite. Nitritation can be obtained by selectively inhibiting the nitrite oxidizing bacteria through appropriate regulation of the system's DO concentration, microbial SRT, pH, temperature, substrate load, operational and aeration pattern, inhibitor and so on. This review addresses the microbiology, its consequences for application, the current status regarding application, and its future developments.

Biological nitrogen removal with nitrification and denitrification via nitrite pathway

Presently, the wastewater treatment practices can be significantly improved through the introduction of new microbial treatment technologies. To meet increasingly stringent discharge standards, new applications and control strategies for the sustainable removal of ammonium from wastewater have to be implemented. Partial nitrification to nitrite was reported to be technically feasible and economically favorable, especially when wastewater with high ammonium concentrations or low C/N ratios is treated. For successful implementation of the technology, the critical point is how to maintain partial nitrification of ammonium to nitrite. Partial nitrification can be obtained by selectively inhibiting nitrite oxidizing bacteria through appropriate regulation of the system's DO concentration, microbial SRT, pH, temperature, substrate concentration and load, operational and aeration pattern, and inhibitor. The review addressed the microbiology, its consequences for their application, the current status regarding application, and the future developments.

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A review of secondary sludge reduction technologies for the pulp and paper industry.

Widespread application of algal biofilm-based systems in wastewater treatment has been limited despite the potential benefits of a low cost nutrient removal option and a source of biomass for bioproduct production. The performance and processes involved with algal biofilm-based systems in wastewater treatment are not adequately addressed in the available literature, which hinders design and scale up of effective systems for applications to municipal, industrial, and agricultural waste streams. A critical review is presented, which examines nutrient removal trends, biomass productivity, growth requirements, and challenges for algal biofilm-based biotechnology as applied to wastewater treatment both at bench scale and at pilot scale operations. Information on algal biofilms in natural environments derived from ecology and limnology disciplines was utilized in areas of limited research with regard to wastewater treatment. This critical review identified key areas that need to be addressed for designing, building, and testing algal biofilm-based technologies that integrate both nutrient removal from wastewater and enhanced biomass production to improve the performance of engineered systems. The review identifies the need for research on factors that affect algal growth, mass transport, species selection, algal–bacterial interactions, and validation of laboratory research in field scale tests for the development of an algal biofilm based technology platform for integrating wastewater treatment and biomass production.

Algal biofilm based technology for wastewater treatment

Long-term effect of dissolved oxygen on partial nitrification performance and microbial community structure.

Alternating aerobic/anoxic (A/A) digestion of waste activated sludge offers many advantages over traditional (aerobic or anaerobic digestion) methods. However, one of the main concerns in A/A digestion is the development of an on-line control strategy for alternating aerobic and anoxic cycles. Computerized pH monitoring has revealed two well-defined control points that correspond to complete nitrification (ammonia valley) and denitrification (nitrate apex). The pH control points were consistent with those previously identified using the oxidation reduction potential. Based on these findings, two real-time control strategies were developed and tested. First, pH was allowed to increase (anoxic) and decrease (aerobic) within preset limits to control A/A cycling. A second approach detected the points of complete nitrification and denitrification using the differential of the pH signal. Comparison of the A/A digestion results with aerobic digesters indicated similar mixed-liquor volatile suspended solids and fecal coliform destruction with aerobic digestion but with better total nitrogen removal and superior dewatering characteristics.

Use of pH as Control Parameter for Aerobic/Anoxic Sludge Digestion

This paper includes reports on several biological fixed film systems in wastewater and hazardous waste treatment. Biological treatment of a refinery wastewater was studied in a rotating biological contactor (RBC) unit coupled with polyurethane foam (PUF) as a porous biomass support attached on both sides of the biodisks. The RBC-PUF bioreactor exhibited better performance than conventional RBCs for the removal of chemical oxygen demand (COD), NH{sub 3}-N, phenol, hydrocarbons, and suspended solids because of higher concentrations of active biomass. Successful performance of an anaerobic-aerobic treatment process using a combination of RCBs with activated sludge was achieved for treating a dye wastewater. Two high-rate trickling filters, cross-flow (CF) and vertical flow, were examined over a two year period for biological treatment of seafood processing wastewater. Results suggested superior performance of CF plastic media with substrate removal following a pseudo half-order kinetic reaction. Submerged structured packings in biofilm reactors were tested and characterized for a wide range of applications. Their efficiency was discussed in terms of contaminant removals and SS retention.

Biological fixed-film systems

Nitrate generated in situ due to nitrification in an aerobic digester was utilized through endogenous nitrate respiration (ENR). This was done by alternating aerobic/anoxic (A/A) cycles. The destruction of volatile suspended solids (VSS) in the A/A system was the same as compared to a controlled-aerobic digester. Approximately 33% of total nitrogen was removed in the A/A system of which 27% was due to ENR during anoxic cycles.



During each anoxic cycle, nitrate reduction was found to be a zero order reaction with respect to nitrate. The specific ENR rates decreased significantly with digestion time due to changes in VSS. Both pH and alkalinity increased during anoxic cycles resulting in enhanced VSS decay and complete nitrification under subsequent aerobic conditions.



The energy savings associated with the A/A system and the use of the specific ENR rates are discussed.

Ibrahim A. Al-Ghusain

Papers

Use of pH as Control Parameter for Aerobic/Anoxic Sludge Digestion

Biological fixed-film systems

Alternating aerobic and anoxic digestion of waste activated sludge

Discussion of "Real-Time Control of Aerobic-Anoxic Sludge Digestion Using ORP"