Physical–anaerobic–chemical process for treatment of dairy cattle manure C. Rico b , H. García a , J.L. Rico a,⇑ a Department of Chemical Engineering and Inorganic Chemistry, University of Cantabria, Los Castros s/n, 39005 Santander, Spain b Department of Sciences and Techniques of Water and Environment, University of Cantabria, Los Castros s/n, 39005 Santander, Spain article info Article history: Received 30 July 2010 Received in revised form 12 October 2010 Accepted 14 October 2010 Available online 20 October 2010 Keywords: Dairy manure Liquid fraction UASB reactor Methane Struvite abstract An overall treatment process for the removal of nitrogen, methane production and obtention of valuable fertilizers from dairy manure has been investigated in laboratory scale. Solid and liquid fractions were separated by flocculation and screening. The solid fraction contained 81.6%, 84.4%, 58.6% and 85.2% of TS, VS, TKN–N and P T originally present in manure. Batch anaerobic digestion of this solid fraction at 50 °C resulted in methane production of 29.0 L CH 4 /kg. The liquid fraction, free of suspended solids, was satisfactorily treated at 35 °C in an upflow anaerobic sludge blanket reactor operating stably at an organic loading rate of 40.8 g COD/(Ld) reaching a methane production of 10.3 L CH 4 /(Ld). Accumulation of volatile fatty acids did not occur. Ammonia nitrogen concentration in the anaerobic effluent fluctuated between 850–1170 mg NH þ 4 –N/L and was reduced to values less than 100 mg NH þ 4 –N/L by struvite precipitation. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Dairy manure is one of the most polluting agro-industrial wastewaters. Intensive dairy farming produces large amounts of manure which, when not properly managed due to its high organic matter, nitrogen and phosphorous concentrations, can cause severe environmental problems such as eutrophication of water bodies (Carpenter et al., 1998), groundwater contamination (Hao and Chang, 2002), air pollution by volatilization of ammonia and other compounds (Ryden et al., 1987) and soil degradation when manure is applied in excess. High concentrations of hazard- ous heavy metals such as Cu 2+ , Zn 2+ and Pb 2+ are not usually present in dairy manure (Nicholson et al., 1999). Land application, the traditional dairy manure management strategy, is nowadays conditioned not only by nutrient requirements of the crops, amount and season, but also by the vulnerability of the near ecosystems and the energy cost for its application (Flotats et al., 2009). In areas with a higher dairy cattle number than avail- able agricultural land for a correctly disposal of dairy cattle manure (one hectare for two milk cattle), another strategy will be neces- sary, such as treatment processes before deposition in the land. When the weather is rainy, and the ground shows pronounced slopes, as it happens in Cantabria, a region in Northern Spain with a bovine population of around 280,000 livestock units (mainly milk), the liquid fraction of dairy manure is a big problem due to run-off, facilitating grow pollution in near ecosystems. Anaerobic digestion of dairy manure has been demonstrated to be an attractive treatment that provides benefits such as pollution control, odour and pathogen level reduction, nutrient recovery and energy production (Amon et al., 2007; Hartmann and Ahring, 2005; Karim et al., 2005; Umetsu et al., 2006). Dairy manure, which has too much suspended solids (SS) content, presents low anaerobic biodegradability. The hydrolytic stage has been identified as the rate-limiting step in the anaerobic digestion of organic particulate slurries such as dairy manure (Gossett and Belser, 1982; Pavlostathis and Giraldo-Gomez, 1991; Vavilin et al., 2002; Veeken et al., 2000). Separation of liquid (LF) and solid (SF) fractions of the waste is a desirable upstream operation in the treatment process. The separated LF, with much less SS content, will require lower temperatures and hydraulic retention times (HRT). However, screened manure presents merely a little more anaerobic biode- gradability because only SS larger than mesh openings have been removed (Kalyuzhnyi et al., 1999). Since the SS content in the LF from screening is still high and only a small fraction of its COD is in soluble form, additional treatments must be performed on screened dairy manure to produce a LF suitable for handling by a high load anaerobic reactor (i.e. in this case HRT could be lower than 1 day). Rico et al. (2007) developed a procedure to obtain a LF from dairy manure to which the major possible quantity of or- ganic matter was transferred, with high anaerobic biodegradability (84%) and free of SS. García et al. (2008) satisfactorily treated this LF in a high load anaerobic reactor (UASB), improving biomass retention into the reactor. The anaerobic digested LF still presents a high ammonia nitro- gen concentration which must be diminished when land area of farm is lower than necessary according to current nitrogen limits 0960-8524/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2010.10.068 ⇑ Corresponding author. Tel.: +34 942201599; fax: +34 942201591. E-mail address: ricoj@unican.es (J.L. Rico). Bioresource Technology 102 (2011) 2143–2150 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech