K.V. Lo

Removal of nitrogen from swine manure wastewaters by ammonia stripping

Abstract Laboratory-scale experiments were undertaken to investigate aeration and air stripping as methods for removing ammonia from swine wastewaters with high nitrogen concentrations. The effects of temperature, air to liquid flow ratio and pH were investigated using wastewaters with a range of solids concentrations and pH values. Five sets of aeration experiments were carried out using two identical 3 l reactors made of acrylic tubing. For the air-stripping experiments, two identical stripping towers were constructed out of acrylic tubing and packed with plastic rings. At a pH of 11·2, the aeration method took approximately 150 h to achieve 90% removal efficiency. This was achieved with temperatures of 22°C and a low air flow rate of 1·15-1·60 l/min. At a comparable pH (11·5), the best results for the air-stripping method achieved 90% removal with only 7 h of treatment. This result was obtained with wastewater temperatures at 22°C, as in the aeration experiment, but the air flow rate was much higher at 90 l/min. Results showed that at a pH of 9·5 and 10·5, ammonia removal efficiency was directly dependent upon the air and liquid influent temperatures. However, at a pH of 11·5 there was no appreciable improvement with a rise in air and influent temperatures. The results further showed that an influent with a low pH required a longer period of time to achieve the same treatment efficiency. A pH of 10·5 is recommended as the most efficient of those tested, as very high levels of nitrogen removal were obtained at that level without incurring problems of excess lime. The high ammonia removal efficiency of the air-stripping method indicates that it could provide an interim solution for current waste management problems in the swine industry.

Aeration experiments for swine waste composting

Abstract A study was undertaken to investigate aeration in the composting of swine manure. Three sets of aeration experiments were conducted to determine the optimum aeration rate. Both continuous and intermittent modes of aeration were tested. Temperature was monitored as the most important indicator of the efficiency and effectiveness of the composting process. Physical and chemical characteristics (moisture content, percent weight loss, total nitrogen, C:N ratio and pH) of compost were also determined. In all experiments except for continuous aeration with rates of 1·0 and 2·0 l/min kg volatile matter, a temperature of 55°C was reached within 2 days and remained above this level for 4–7 days, thus satisfying the regulatory requirements for a PFRP (Process to Further Reduce Pathogens). The results indicated that the temperature of the compost pile was controlled by the aeration rate in combination with the frequency and the duration of aeration. It is recommended that an aeration rate of 0·04–0·08 l/min kg volatile matter and an intermittent mode of aeration should be adopted for swine manure composting.

Anaerobic treatment of brewery wastewater using UASB reactors seeded with activated sludge

Abstract In this study, two upflow anaerobic sludge blanket (UASB) reactors seeded with aerobic activated sludge were used to treat brewery wastewater. The reactors were identical in design and were continuously operated at 19–24°C. Reactor A was seeded with 1·98 g volatile suspended solids (VSS) per liter of acclimatized activated sludge, while Reactor B was seeded with 1·98 g VSS l−1 of acclimatized sludge and 3·95 g VSS l−1 of unacclimatized sludge (a total of 5·93 g VSS l−1). The study examined reactor performance in terms of treatment efficiency and methane production under different hydraulic retention times (HRT) and organic loading rates, and evaluated the effect of amount of seed sludge on reactor start-up and performance. The results indicate that as the chemical oxygen demand (COD) loading rate increases with time, the influence of the amount of seed sludge becomes more pronounced. Reactor B consistently out-performed Reactor A under shorter HRTs of 1·5 days to 12 h with maximum COD and VSS removal rates of 91% and 81%, respectively, at a sludge loading rate of 0·25 g COD g−1 VSS day−1 and an HRT of 18 h. The results also confirm that an acclimation period of at least 2 weeks is necessary to prevent delays in the start-up process when using activated sludge as seed. Using 5·93 g VSS l−1 of activated sludge as seed enabled Reactor B to achieve satisfactory performance.

Digestion of cheese whey with anaerobic rotating biological contact reactors

Abstract A laboratory-scale anaerobic rotating biological contact reactor receiving full strength cheese whey was studied over a range of hydraulic retention times from 11 to 5 days at 35°C. Methane production rates ranging from 1·68 to 3·26 litres CH 4 litre −1 and a 76 to 93% reduction in chemical oxygen demand were achieved. At hydraulic retention times shorter than 5 days, steady-state operation could not be maintained for reactors receiving either full strength or diluted whey. A two-stage fermentation system was also studied; the results indicated that stable operation and treatment efficiency (89·5% COD removal) could be achieved.

Anaerobic treatment of swine wastewater using hybrid UASB reactors

Abstract Two hybrid upflow anaerobic sludge blanket (UASB) reactors were used to treat screened swine wastewaters. In order to achieve the advantages of both suspended growth and attached-growth anaerobic reactor systems, this type of reactor has a rope matrix inserted as a fixed-film medium in its mid section. The study examined the reactor performance in terms of its treatment efficiency and membrane production, and evaluated the effect which the absence of seeding in the start-up process had on the efficiency of reactor performance. The conclusion reached was that this hybrid UASB reactor could be used without seeding in the treatment of screened swine manure if the organic loading rates were moderate. Under these conditions, over 57% COD removal and 0.71 litres CH 4 /litre reactor day were obtained. While sludge loss did occur, methane production increased and the concentrations of VFA in the effluents were kept below 100 mg/litre. It is believed that the additional biofilm in this hybrid reactor increased the stability of the reactor and helped maintain steady methane production. The results also confirm that granulation of the sludge is an essential requirement for satisfactory operation.

Real-Time Control of Two-Stage Sequencing Batch Reactor System for the Treatment of Animal Wastewater

An evaluation of the use of ORP as a real-time control parameter was conducted. A newly developed real-time control strategy, using ORP, was successfully applied, without a supplemental carbon source, to a new type of bench-scale two-stage SBR process for the treatment of swine wastewater. With real-time control, consistently high system performances were obtained, despite the fluctuation of influent quality; removal efficiencies for BOD5, COD, NH4-N, TKN, Ortho-P, Total Phosphorus (TP) averaged approximately 99.6%, 97%, 98%, 96%, 95% and 94%, respectively. Also, effective denitrification could be achieved without the addition of an external carbon source; the average NOx-N level on final effluent was 11 mg l−1. The data from this study reveal that both the ORP and pH can be used as successful process control parameters in the optimization of nutrient removal and treatment system capacity. Feasible real-time control strategies using dynamic ORP and pH change are established through this research.

A hydrogen peroxide/ microwave advanced oxidation process for sewage sludge treatment.

This study focused on the efficacy of the microwave/hydrogen peroxide advanced oxidation process (MW/H2O2–AOP) on the secondary sludge treatment. The results indicated that at temperatures of 80°C and above, essentially all of the chemical oxygen demand (COD) was solubilized by the combined MW/H2O2–AOP. This process also solubilized nutrients (nitrogen, phosphorus and metals) from sludge which can be extracted for other purposes, such as struvite crystallization. Based on a stoichiometric molar ratio of 1:1:1 for Mg:NH3:PO4, ammonia was found to be the limiting nutrient without any H2O2 addition in the process at all temperatures. With the addition of H2O2, ortho-phosphate became the limiting nutrient. In all treatments, magnesium was non-limiting, thus magnesium addition is not required for subsequent struvite crystallization. The MW/H2O2–AOP also enhanced the pasteurization or sterilization of sludge. The MW/H2O2–AOP provides novel sludge management options for the wastewater industry, not only in solubilization of carbon for further methane production, but also in nutrients extraction for crystallization for use as fertilizer.

Advanced Oxidation Process Using Hydrogen Peroxide/ Microwave System for Solubilization of Phosphate

An advanced oxidation process (AOP) combining hydrogen peroxide and microwave heating was used for the solubilization of phosphate from secondary municipal sludge from an enhanced biological phosphorus removal process. The microwave irradiation is used as a generator agent of oxidizing radicals as well as a heating source in the process. This AOP process could facilitate the release of a large amount of the sludge-bound phosphorus from the sewage sludge. More than 84% of the total phosphorous could be released at a microwave heating time of 5 min at 170°C. This innovative process has the potential of being applied to simple sludge treatment processes in domestic wastewater treatment and to the recovery of phosphorus from the wastewater.

Sewage sludge nutrient solubilization using a single-stage microwave treatment

The effects of an advanced oxidation process combining microwave, hydrogen peroxide and acid hydrolysis in a single stage (MW/H2O2/H+-AOP) on the process efficiency of sewage sludge treatment and nutrient recovery were investigated. At lower temperature regimes (60–80°C), the soluble phosphate was substantially higher in a two-stage process than in a single stage MW/H2O2/H+-AOP process. However, higher soluble phosphate concentration was obtained for single-stage treatment at the higher operating temperature regimes (100–120°C). With the addition of an inorganic acid, a very high yield of soluble phosphate was obtained in the solution at 120°C. In tests with acid addition, soluble ammonia increased as temperature increased. For single stage MW/H2O2/H+-AOP, maximum soluble ammonia was obtained at 120°C. Significant concentrations of soluble COD were also obtained in this treatment. A threshold temperature of 80°C was observed, at which all of the COD could be solubilized. However, at higher temperatures (100–120°C), further oxidation processes occurred to form carbon dioxide, resulting in decreased amounts of soluble COD in the solution.

AMMONIA REMOVAL FROM COMPOSTING LEACHATE USING ZEOLITE. I. CHARACTERIZATION OF THE ZEOLITE

The effects of ammonium concentrations, contact time, and zeolite particle sizes on the ammonium adsorption capacities of a Canadian zeolite were studied using batch experiments. Both the rates and capacities of ammonium adsorption increased with increased concentrations of ammonium in solution. Ammonium adsorption increased significantly with decreasing zeolite particle size for all tests and the adsorption capacities ranged from 14.35–17.81 mg N/g. Also, ammonia adsorption increased with contact time, and it occurred rapidly at the beginning of contact, and then gradually decreased as time progressed. Langmuir isotherm best describes the equilibrium of ammonia adsorption on zeolite. Particle diffusion was the rate-controlling mechanism for the first 4 h of contact. In spite of competition potassium ions, zeolite has shown a great potential for ammonia removal from composting leachates.