G. K. Anderson

Interference of hydrogen peroxide on the standard cod test

Abstract The standard method for measuring chemical oxygen demand (COD), which is widely used throughout environmental engineering is affected by a number of inorganic substances. These are outlined in Standard Methods (APHA, Standard Methods for the Examination of Water and Wastewater, 16th edition, Washington, D.C., 1985) and methods of overcoming the problems are given, however, no reference is made to hydrogen peroxide as an interfering substance. In a number of complex industrial wastewaters, H2O2 is present and is also used in its treatment which will thus interfere with the analysis. This interference has a positive error effected on COD. This work has been carried out in order to show how hydrogen peroxide interferes in COD analysis, and further shows how to allow for this interference in future COD analysis. A number of specific points have been raised. It has been shown that H2O2 forms a complex with potassium dichromate, the structure of which is given. In experiments which were made on a range of synthetic samples, it was noted that the samples containing H2O2 had different COD values for various concentrations although they contained no organic substances. Also, it was shown on industrial wastewater samples that H2O2 either increased the COD values of the wastewater samples or interfered with the procedure, by completely masking the titration end-point. Reference is made to those industries and processes which contribute to interference by H2O2. A method of calculating the effect of interference by H2O2 is recommended.

The effect of polymer addition on granulation in an anaerobic baffled reactor (ABR). Part II:: compartmentalization of bacterial populations

The microbial ecology of wastewater treatment plants remains one of the least understood aspects in both aerobic and anaerobic systems, despite the fact that both processes are ultimately dependent on an active biomass for operational efficiency. Ultimately, future developments in anaerobic treatment processes will require a much greater understanding of the fundamental relationships between bacterial populations within the biomass if optimum process efficiency is to be fully realised. This study assesses the influence of polymer addition on granule formation within an ABR and compares the ecology of the biomass in each compartment of two ABRs treating ice-cream wastewater. To our knowledge, this is the first reported characterisation of the microbiology of acidogenic and methanogenic bacteria in the individual compartments of an ABR. The polymer-amended reactor contained sludge that had a greater density of anaerobic bacteria and larger and denser granules than the control reactor, indicating that polymer addition possibly contributed to the retention of active biomass within the ABR. The average fraction of autofluorescent methanogens was lower, with 1.5% being in the initial compartments of the ABRs, compared to the last compartment which had 15%, showing that each compartment of an ABR had a unique microbial composition. Partial spatial separation of anaerobic bacteria appeared to have taken place with acidogenic bacteria predominating in the initial compartments and methanogenic bacteria predominating in the final compartments. Scanning electron micrographs have revealed that the dominant bacteria in the initial compartments of the ABR (Compartments 1 and 2) were those which could consume H2/CO2 and formate as substrate, i.e. Methanobrevibacter, Methanococcus, with populations shifting to acetate utilisers, i.e. Methanosaeta, Methanosarcina, in the final compartments (Compartments 3 and 4). In addition, there appeared to be a stratified structure to the bacterial genera present within the granules.

The effect of polymer addition on granulation in an anaerobic baffled reactor (ABR). Part I: process performance.

The stability and performance of an anaerobic baffled reactor (ABR) treating an ice-cream wastewater at several organic loading rates have been investigated. Specifically, it was determined whether an ABR would promote phase separation and if a polymer additive was capable of enhancing granule formation in an ABR. In order to achieve these goals, two ABRs, having identical dimensions and configurations, were used to study the above objectives using a synthetic ice-cream wastewater. The ABR proved to be an efficient reactor configuration for the treatment of a high-strength synthetic ice-cream wastewater. An organic loading rate of around 15 kg CODm(-3) d(-1) was treated with a 99% COD removal efficiency. From the jar test and inhibition assay, it was concluded that Kymene SLX-2 was the most effective and least inhibitory polymer tested. The methane yield was higher in the polymer-amended reactor compared to the control reactor. In addition, polymer addition resulted in a considerably higher degree of biomass retention and lower solids washout from the ABR. Consequently, it demonstrated that there was a considerable potential for sludge conditioning in ABRs by facilitating better biomass retention within the reactor which in turn led to better process performance. Granulation was achieved in both ABRs within 3 months. However, the granules from the polymer-amended reactor appeared earlier and were generally larger and more compact, although this was not quantified in detail during the present study. The main advantage of using an ABR comes from its compartmentalised structure. The first compartment of an ABR may act as a buffer zone to all toxic and inhibitory material in the feed thus allowing the later compartments to be loaded with a relatively harmless, balanced and mostly acidified influent. In this respect, the latter compartments would be more likely to support active populations of the relatively sensitive methanogenic bacteria and partly explains why the best granules and the highest methane yield were obtained in Compartment 2. It is unlikely that a complete separation of phases (acidogenic and methanogenic) occurred within the ABRs since methane production was observed in all compartments, although this was low (approximately 40% of all gas composition) in Compartment 1, becoming higher (approximately 70%) in the following compartments.

Control of organic loading rate using the specific methanogenic activity test during start-up of an anaerobic digestion system

The specific methanogenic activity test (SMA) was used to determine a suitable organic loading rate during the start-up phase of a crossflow ultrafiltration membrane anaerobic reactor system (CUMAR). The SMA test was immediately carried out after seeding the reactor with sludge taken from a municipal wastewater treatment plant digester in order to determine the most acceptable initial organic loading rate. The initial test results during the first week showed that the acetoclastic capacity of the reactor sludge, at an organic loading rate (OLR) of 1 kg COD/m3 · d, was found to be low which resulted in a very poor COD removal efficiency, i.e. 14%. Therefore the OLR was maintained at approximately 0.7 kg COD/m3 · d in the next two weeks of operation resulting in the COD removal efficiency of over 65% in the effluent. Based upon the SMA tests results, the OLRs were either increased or decreased in order to improve performance of the system and to achieve stable conditions which further resulted in an excellent organic matter removal, i.e. over 98% COD and almost 100% BOD removal at an OLR of over 1 kg COD/m3 · d. At this point the ratio of actual methane production (AMP) rate of the CUMAR system to potential methane production (PMP) rate determined from the SMA test was 0.45, which ensured that the CUMAR system could be loaded at higher organic loading rates for the remainder of the operating period.

High rate aerobic treatment of brewery wastewater using the jet loop reactor

Abstract An aerobic Jet Loop Reactor (JLR) activated sludge process of 541. volume was used to investigate its suitability for the treatment of industrial wastewaters, specifically brewery wastewater. A loading rate of 50 kg COD/m 3 ·d was achieved with 97% COD removal for a period of 5 weeks and although the settleability was found to be acceptable non-flocculating motile bacteria caused the effluent to be cloudy and have a high suspended solids concentration in the order of 200–350 mg/l. Investigations into how this loading rate was achievable and its consequences included measurements of oxygen transfer rate, Specific Oxygen Uptake Rate (SOUR), determination of Monod kinetic coefficients and microscopic examination. Oxygen transfer rates were found to be high, with a low energy efficiency possibly due to the small scale of the rig, SOUR values varied between 100–400 mg O 2 /g VSS·h for F/M ratios of 5–8 kg COD/kg MLVSS·d and the maximum growth rate was found to be 12.2/d with a yield of 0.4 kg VSS produced/kg COD removed. Although the Jet Loop Reactor was found to be a suitable method for pretreating brewery wastewater, an effluent polishing stage before final discharge to a water course would be necessary and it was concluded that further investigations into jet design may increase the oxygen transfer efficiency and quality of effluent.

Microbiological study of two-stage anaerobic digestion during start-up

Abstract The changes in the microbial population of a two-stage anaerobic digestion system in terms of number and composition were studied during the start-up phase. The numbers of methanogens and non-methanogens slightly decreased in the upflow filter, whereas in the pre-acidification stage the number of acidogens was reasonably constant. Variations in the morphology of the methanogens occurred along the filter, for example the numbers of Methanosarcina and filamentous bacteria species decreased considerably in the drain, possibly becoming attached to the biofilm along the reactor, whereas in the pre-acidification stage only a few Methanosarcina species were identified. Slight variations within the bacterial populations occurred in terms of composition and numbers in the filter. The number of viable methanogens varied in the filter effluent depending on the OLR changes but this did not adversely affect the COD removal efficiency of the upflow filter. Among the autofluorescent methanogenic population, Methanococcus, Methanobacterium, Methanobrevibacteria , and Methanosarcina species were tentatively identified in the filter.

Inert COD production in a membrane anaerobic reactor treating brewery wastewater

Abstract In this study, inert COD production in a crossflow ultrafiltration membrane anaerobic reactor (CUMAR) system treating brewery wastewater, was investigated. The system was operated at a wide range of influent chemical oxygen demand (COD) concentrations and solid retention times (SRT) in order to determine residual non-biodegradable COD produced by biomass in the anaerobic reactor. Previous studies showed that the wastewater had practically no inert soluble COD. The inert soluble COD in the effluent would, therefore, have been produced in the anaerobic reactor by the biomass. Significant increases in the effluent COD concentration were observed during the operation of the CUMAR system at SRT lower than 100 days. It was also calculated from the results that the soluble microbial products measured in terms of COD were found to be an average of 2.2% of the influent COD. These microbial products were not removed from the effluent even with extended operation times. Throughout the operation, a maximum of 28.5 kg COD/m 3 day was applied, at which point COD removal efficiencies of no lower than 97% in the anaerobic reactor and 99% in the membrane permeate were achieved during the steady-state operation of the CUMAR system.

Comparison of porous and non-porous media in upflow anaerobic filters when treating dairy wastewater

Abstract The performance of porous and non-porous media in two mesophilic anaerobic upflow filters treating a wastewater from a milk bottling factory was investigated. The results indicated that at higher OLRs the porous media had a much better performance. The reactor with non-porous packing showed instability above an OLR of 4 kg COD/m3 ·d whereas the reactor with the porous packing was still stable at OLRs of up to 21 kg COD/m3 ·d. The behaviour of the media and biomass wash-out were observed at high upflow velocities (UV) and results demonstrated that porous media was not as susceptible to shear stresses as non-porous media. At the end of the investigation, attachment studies were carried out and the results showed a heavy biomass attachment in the porous media, whereas mainly unattached biomass was retained in the voids of the non-porous media.

Oil/Water separation with surface modified membranes

Abstract This study examines the feasibility of designing a membrane surface which would enhance the separation of oil from oil/water suspensions using crossflow filtration. The surface characteristics of both Ultrafiltration and microfiltration membranes were modified by adsorption with a surfactant, resulting in significant improvement in oil rejection.

Composition of the microbial population in a membrane anaerobic reactor system during start-up

Abstract Changes in the numbers and the composition of the microbial population in a pilot-scale membrane anaerobic reactor system were studied during 14 weeks operation. The membrane reactor was inoculated with the sludge taken from a digester of a municipal wastewater treatment plant. An initial epifluorescent microscopic examination of the seed sludge revealed that the most dominant group was Methanococcus followed by Methanosarcina , short rods, medium rods, filaments and long rods. Changes in the composition of the dominant methanogenic species were observed throughout the operation. Methanococcus species were found to be the most dominant group at the end of the study followed by medium rods, short rods, Methanosarcina , long rods and filamentous species. The numbers of both methanogens and non-methanogens were found 50% and 20% increased in the reactor after 14 weeks operation while the numbers of viable methanogens sharply increased, i.e. 20 times, resulting in a 50 times increase in the metabolic activity of the fluorescent methanogens. Within the fluorescent methanogenic population, Methanosarcina, Methanococcus, Methanobacterium and Methanobrevibacteria species have been tentatively identified. Acclimatization of the digester sludge was completed after 40 days operation after which the COD removal efficiency of the system was found to be over 98% showing that a satisfactory microbial population had been established in the digester