Eleven years of composting biosolids in Bariloche (Patagonia, Argentina).

MAZZARINO, M.J.; SATTI, P.; LAOS, F.; ROSELLI, L.; FERNANDEZ, H.

Heraklio

Congreso; 7th Intern. Conference ORBIT2010 "Organic Resources in the Carbon Economy”; 2010

ORBIT

Because of the lack of national regulations on wastewater treatment, the number of treatment plants is still low in Argentina, and those with an advanced system (secondary or tertiary) are restricted to small cities, mostly with fewer than 100,000 inhabitants. The city of San Carlos de Bariloche, known as the capital of the southern lakes area, is located in the Nahuel Huapi National Park, between the piedmont of the Andean Mountains and the transitional ecotone to the semiarid steppe, in NW Patagonia (41º05’S, 71º20’W). It is a non-industrial resort community with about 130,000 permanent inhabitants and 500,000 tourists per year, surrounded by winter ski centers, glacial lakes and temperate forests. Wastewaters have been discharged directly into Lake Nahuel Huapi for almost 100 years. Since 1996, an extended aeration activated sludge plant depurates 70% of the effluents, yielding about 3,000-4,000 m3 of biosolids per year (12-15% solid content). Based on research conducted by the Soil Science Staff of the Universidad Nacional del Comahue, in 1997 the Electricity Cooperative of Bariloche constructed the city’s first Biosolids Composting Plant. It occupied 2 ha on a site located 12 km outside town, and it operated until 2005, when it was replaced by a 2nd plant on a larger site. Controls of the process and end-product quality were entrusted to the Soil Science Staff. The first composting plant was also the first such facility in Argentina that met international standards. About 200-300 m3 of biosolids are composted monthly in windrows (10-15 m long, 3-4 m wide and 1.6 m high) mixed with woodshavings and yard trimmings as bulking agents. Windrows are formed and turned with a front-end loader. To achieve temperatures required by international regulations for pathogen reduction, a 1:1-2 biosolids:bulking agent ratio is employed. The region is characterized by dry, warm summers and cold, humid winters, so more bulking agent is needed during winter. The composting process (thermophilic and maturation phases) lasts about 8 months. The compost is sold unscreened or screened with 0.5 cm mesh. Bariloche’s compost meets USEPA Part 503 Class A exceptional quality standards; since it is mainly a resort city, hardly any industrial facilities are connected to the wastewater system; consequently trace element concentrations are very low. During the first 2 years trace elements were analyzed monthly in biosolids before composting; since then they have been measured every 3 months, and currently every 6 months in biosolids and composts. As stabilization and maturity indicators, ammonium, nitrates, water soluble C, WSC/total N and germination tests are assessed. Compost quality is tested through analysis of pH, soluble salts, total and available N and P, total C, Ca, Mg and K, and mineralization and respiration assays. Composts have been tested in greenhouse and field trials with native and exotic grasses, ornamental and tree species, restoration experiments of ecosystems degraded by overgrazing and wildfires, and bioremediation of petroleum-contaminated soils. At the local and regional levels, they are employed for roadside vegetation establishment, ornamental and tree nurseries, turf grass, and landscaping. Public acceptance during the first years was low, and large piles of mature compost accumulated in the composting plant, leading to contamination with seeds from the surrounding vegetation. After several years of extension lectures, and result transfer in schools and public centers, the demand increased resulting currently in the complete sale of the yearly production. Main constraints of this facility are transport costs of biosolids (composting facility is far from the treatment plant), availability of bulking agents (especially in winter), and thievery: machines are transported daily which increases operating costs, and open roof construction or plastic covers can not be used which constrains infrastructure improvement. This experience is a good example of cooperation between a public institution and a private firm in a developing country, working even during harsh economic times (300% monetary devaluation). Since national regulations are still provisory or inexistent, our experience in Bariloche is used by all those interested in composting biosolids. Based on it, composting plants have been constructed in Mar del Plata (Buenos Aires province) and Corrientes province, and numerous technicians and researchers of Argentina and Chile have been trained..