Iwa international Specialist Conference

 

J.-Y. Wang, O. Stabnikova, H. Ding, S.T.-L. Tay, V. Ivanov, and J.-H.Tay

Environmental Engineering Research Centre, School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore

 Sewage sludge and food wastes consist of important nutrients and can be used in agriculture. More than 50,000 tons of sewage sludge and 100,000 tons of food wastes are produced in Singapore but only small portion of the wastes is recycled. An aim of our research is the development of biotechnology for intensive aerobic bioconversion of sewage sludge and food waste into fertilizer avoiding the phases of curing and maturation of conventional composting. The wastes were treated in a closed reactor under controlled aeration, stirring, pH, and temperature 60^oC, after addition of starter bacterial culture. Starter culture was selected by the growth rate on the sewage sludge as a source of the nutrients. It was identified by 16S rDNA gene sequencing as Bacillus thermoamylovorans. The biodegradation of sewage sludge, which is mainly anaerobic microbial biomass, was studied by decrease of volatile solids (VS), content of organic carbon, autofluorescence of coenzyme F₄₂₀, the quantification of specific binding of Archaea-specific oligonucleotide probe Arc915. The bacteriological quality of the product was also studied by the enumeration of enterobacterial cells by flow cytometry after whole cell, in situ hybridization with the specific oligonucleotide probe targeted to 16S rRNA. Significant portion of enterobacteria survived notwithstanding the two weeks of the treatment at 60^oC. The degradation of anaerobic biomass was faster than biodegradation of total organic matter. The best fertilizer was obtained when sewage sludge was thermally pre-treated, mixed with food waste, chalk, and artificial bulking agent. The content of volatile solid and the content of organic carbon decreased at 24.8% and 13.5% total solids, respectively, during ten days of bioconversion. The fertilizer was a powder with moisture content 5%. It was stable, and not toxic for the germination of plant seeds. Addition of 1.0 – 1.5% of this fertilizer to the subsoil increased the growth of different plants by 113 –164 %. The biotechnology can be applied in larger scale for the recycling of sewage sludge and food wastes in Singapore.

40.

Assessing Nutrients Availability of Irradiated and Non-Irradiated Biosolids for the Agriculture Re-use.
Cecilia MAGNAVACCA and Monica SANCHEZ.
Technological and Agriculture Applications, Ezeiza Atomic Center, Comisión Nacional de Energía Atómica (CNEA), Argentina.

ABSTRACT

Biosolids generated by municipal wastewater treatment processes are a source of disease-causing organisms that include bacteria, viruses, protozoan cysts, and helminthes ova. Even after aerobic or anaerobic digestion for extended periods of time, the sludge will still contain pathogens. If the sludge is to be land applied for crop production, then further treatment is needed to inactivate pathogens and to reduce the risk to public health. Irradiation provides a fast and effective means to disinfect sewage sludge and its reliability in inactivating pathogens has been tested in many countries

The CNEA (Argentina) has carried out the project for design, construction and demonstration of a biosolids irradiation prototype plant. The location of the plant is within the Tucuman City (Northwestern Argentina) Wastewater Treatment Plant, which performs primary type process and anaerobic digestion of sludges. The City is centered on an eminently agriculture zone, 80% for sugarcane cultivation. Design characteristics and construction details of the Plant may be found in previous literature. The research about further uses of the irradiated biosolids has focused several topics including sludge characterization, irradiation effects on sludge physico-chemical properties, agriculture re-use recommendation and limitation of irradiated sludge based on toxics contents, and perspective of long-term effects of the biosolids application on Tucuman's soil.

It is known that biosolids are sources of Nitrogen and Phosphorus nutrients, mainly available N source for N-dependent crops, like sugarcane is; but some benefits of the irradiated biosolids application on the crop yield are still discussed. The chemical integrity of some substances in the biosolids may be altered by the radiation treatment, thus change the availability of plant nutrients. Wen et al. (1995) had reported that the plant-available N of sewage sludge increased after the irradiation. However, the consequent increase in crop yield due to the N available release during irradiation, was not consistent in the results of several authors.

Chemical analyses were done with anaerobically digested sludges with and without irradiation process. The experimental irradiations were made at the Semi-Industrial Irradiation Plant of the Ezeiza Atomic Center; the radiation absorbed dose was, as convened for satisfactory disinfection effect, 3 kGy (wet sludges) to 5 kGy (semi-dried sludge). P chemical forms and their composition in sludge were not affected, neither total N content; but the NH₄-N content of the irradiated sewage sludge increased by 3% and its organic N content proportionally decreased.

Another laboratory experiment (simple respiration experiment) was done with sealed flasks containing soil, biosolid ammended soil and irradiated biosolid ammended soil, including a little vial with Potassium Hydroxide, that will be combined with CO₂ generated by microorganisms respiration. At regular periods, the remaining hydroxide is evaluated by titration; the accumulated data are indication of the bacteria mineralization activity in the sludge. This resulted to be higher in soil with irradiated biosolid than with non-irradiated one.

Chemical evaluations of available-N in soil samples of a field experiment at Ezeiza Atomic Center were done following the usual design: control soil, soil + chemical fertilizer, soil + biosolid (I,II,III,IV rates equivalent to 3,6,9,12 ton/ha), soil + irradiated biosolid (I,II,III,IV rates), four replicates each one. The increasing amounts of N-Nitrate were always higher in irradiated biosolids ammended soils compared to the non-irradiated ones, except in the maximum (exaggerated) rate.

Using the same scheme as above, a lettuce crop field experiment was carried out with measurements of dried matter from harvested material. The results were consistent to the previous experiments.

The two major experiments were made at Tucuman's field of sugarcane annual crop: one beside the other one, both using biosolids obtained from the Tucuman Wastewater Treatment Plant. Sugarcane total biomass was evaluated, and parts were extracted for further analyses. The experiments were repeated three years. The difference in both experiments was that the biosolids were ground to almost powder (the particle size score is shown) before the application on soil, in one of the experiments. The same was done for the described lettuce experiment. The results were comparable to the lettuce crop yield proportions. For the other experiment, the biosolids were applied in bulk of bigger pieces; the results then were not satisfactory and no difference was found between irradiated and non-irradiated material.

CONCLUSIONS.

It is suficiently demonstrated that the irradiation treatment, at doses for only disinfection effect, causes links breaking in the organic chemical matrix, and a release of available Nitrogen. Then, a major benefit is foreseen in the application of irradiated biosolids for the type of crops that incorporates mineralized forms of N.

Probably this beneficial effect is neutralized and is not seen, when large amount of biosolids (more than 10 ton/ha) are applied; then the immobilization effect, due to the large amount of organic materia to be decomposed by bacteria, could be stronger than the mineralization and nutrition activities of the microorganisms for the plant. For this reason, and to avoid unnecesary charge of toxics on soil, the application rate of biosolids should be carefully limited.

It is also evident the importance of the small particle size of biosolids during the application for complete mixture and incorporation to soil. *******************

41|

Elimination of Linear Alkylbenzene Sulfonate (LAS ) and SOAP DURING composting OF ANAEROBIC SLUDGE.
Prats D., Rodriguez M., Muela M.A., Llamas J.M. - University of Alicante – Spain⁽¹⁾

Moreno A., De Ferrer J, Berna J.L. - Petresa – Spain⁽²⁾.
ABSTRACT
The composting plant uses a variety of agricultural residue and sludge from nearby wastewater treatment plants. The results obtained indicate a very high removal of LAS (> 97%) in a very short period of time while the removal of soap was substantially lower (32%) as well as the elimination of TOC (total organic matter). The average half life of LAS in the process was between 6 and 9 days which is very short compared to the average residence time of the feed in the composting process (40 days).
NB !!

A whole paper (12 pages) was sent in. Only the short abstract is included here

42.

A two-stage configuration for the anaerobic digestion of the production of sludge generated during the production of bioethanol from sweet sorghum