Pollution reduction at wastewater treatment facilities through thermophilic sludge digestion

Wastewater treatment facilities produce large amounts of sludge, which is a pollutant to the environment if not properly managed. Among the three most common methods (landfills, land application, incineration) of sludge disposal, thermophilic digestion to produce Class-A biosolids for land application is recognized as the most cost-effective, environmentally sustainable option. Full-scale experience revealed that thermophilically digested biosolids consumed a higher dosage of chemicals for conditioning and dewatering than conventionally (mesophilically) digested biosolids. This paper presents findings of a recent study to investigate how major operational parameters affect dewatering properties of thermophilically digested biosolids, and to search for the inter-relationship between digestion, characteristics of digested biosolids, and dewatering properties of thermophilic biosolids. Experimental work was carried out using bench-scale aerobic digesters. This study found that feed sludge composition has a significant effect on dewaterability. A higher content of secondary sludge resulted in poorer dewaterability in undigested and digested sludge. Dewatering properties are sensitive to a temperature effect. Such an effect is physical-chemical in nature. Excessive high shear results in significant deterioration in dewaterability. Thermophilic digestion resulted in a substantial increase in ammonia and phosphate concentrations, but these two factors seem to not have much impact on dewaterability. Instead, cellular biopolymers have a significant role in affecting dewatering properties of thermophilically digested biosolids.</jats:p

Ammonia Removal from a Landfill Leachate by Nitrification and Denitrification

Abstract The purpose of this research project was to study the biological treatability of a leachate from an “older” landfill, with specific regard to the removal of ammonia by nitrification and denitrification. A single sludge denitrification system with recycle was used. Leachate ammonia concentrations of up to 288 mg/L-N were reduced to less than 1 mg/L. The ammonia was removed by nitrification and bacterial uptake. Glucose was added to aid denitrification. The degree of denitrification was dependent on the glucose loading to the anoxic reactor. The influent leachate COD removal was 20%; however after the addition of glucose to the system, a mean COD removal of 74% was obtained. The four metals monitored, zinc, manganese, nickel and iron were removed by the biomass, but not to the same extent. At the metal concentrations observed, there was no inhibitory/toxic effect to the ammonia removal system employed.</jats:p

Treatment of a Municipal Leachate Under Multi-Variable Conditions

Abstract The treatability of a municipal leachate (BOD5 = 8090 mg/L) was investigated, by aerobic biostabilization, at a nutrient loading of BOD5:N:P of 100:3.2:1.1. The first stage effluents were subsequently polished by lime-magnesium coagulation. The ranges of ambient air temperature and sludge age studied were 5° to 25°C and 5 to 20 days, respectively. In the biostabilization phase, a BOD5:N:P loading of 100:3.2:1.1 was found to be “adequate” for treatment. Organic and metal removals in the first stage units were excellent. Under all conditions investigated, except for the two units close to washout conditions (5-day sludge age units at 5° and 10°C), BOD5 and COD removals of at least 99.4 and 96.4 percent, respectively, were achieved. Similarly, removal rates for most of the metals monitored were greater than 90 percent. In general, the removal of residual contaminants was not enhanced significantly by the addition of magnesium in the lime-magnesium polishing step.</jats:p

Influent Constraints on Treatment and Biological Nitrification of Municipal Landfill Leachate

Abstract A laboratory-scale treatment process was set up to treat Port Mann Landfill leachate, a high ammonia, low degradable carbon leachate with occasional high metals. A single sludge, nitrification/denitrification system was run for 25 weeks, with methanol added as a carbon source to improve denitrification. The objective of the treatment process was to remove biodegradable carbon and ammonia (feed levels of 25 to 250 mg/L). Carbon removal, including methanol, was adequate at SRT's of 10 days or greater. An SRT of 5 days produced inadequate treatment. Of the metals of concern, all except nickel were concentrated in the biomass. Ammonia removal was inconsistent. Good nitrification occurred at the start of the study but no denitrification occurred until operating conditions were optimized. Both processes deteriorated as the study progressed. The study clearly demonstrated that changing influent characteristics constrained the overall treatment of the leachate.</jats:p

Leachate Production and Characteristics as a Function of Water Input and Landfill Configuration

Abstract A field sampling programme was carried out at a Vancouver Lower Mainland landfill to study leachate flow and characterization. A water balance and simple hydrogeologic model were developed for the site In order to calculate leachate discharge rates. Details of leachate composition are presented and related to site water input patterns. The interdependance of leachate composition, water input and fill retention time is hypothesized. Implications are presented in terms of site configuration and treatment process design.</jats:p